From cdcde661efe4e59c19d1a669f09a0842fb742e90 Mon Sep 17 00:00:00 2001
From: Leonardo de Moura <leonardo@microsoft.com>
Date: Sat, 25 Oct 2014 13:36:38 -0700
Subject: [PATCH] feat(library/definitional/induction_on): automatically add
 'induction_on'

---
 library/data/list/basic.lean                  |   4 -
 library/data/nat/basic.lean                   |   4 -
 library/data/num.lean                         |   8 -
 library/data/option.lean                      |   4 -
 library/data/vector.lean                      |   4 -
 library/hott/equiv.lean                       |   2 +-
 library/hott/path.lean                        | 208 +++++++++---------
 library/logic/decidable.lean                  |   2 -
 src/frontends/lean/inductive_cmd.cpp          |   2 +
 src/library/definitional/CMakeLists.txt       |   2 +-
 src/library/definitional/induction_on.cpp     |  48 ++++
 src/library/definitional/induction_on.h       |  19 ++
 src/library/definitional/rec_on.h             |   2 +
 .../lean/interactive/findp.input.expected.out |   1 +
 .../lean/interactive/num2.input.expected.out  |   3 +
 tests/lean/run/beginend2.lean                 |   6 +-
 tests/lean/run/get_tac1.lean                  |   4 +-
 tests/lean/run/lift.lean                      |   2 -
 tests/lean/run/nat_bug.lean                   |   2 -
 tests/lean/run/nat_bug5.lean                  |   1 -
 tests/lean/slow/nat_bug2.lean                 |   3 -
 tests/lean/slow/nat_wo_hints.lean             |   5 -
 tests/lean/slow/path_groupoids.lean           | 200 ++++++++---------
 23 files changed, 281 insertions(+), 255 deletions(-)
 create mode 100644 src/library/definitional/induction_on.cpp
 create mode 100644 src/library/definitional/induction_on.h

diff --git a/library/data/list/basic.lean b/library/data/list/basic.lean
index 768d7db9bf..84db7b4393 100644
--- a/library/data/list/basic.lean
+++ b/library/data/list/basic.lean
@@ -21,10 +21,6 @@ notation `[` l:(foldr `,` (h t, cons h t) nil) `]` := l
 
 variable {T : Type}
 
-protected theorem induction_on {P : list T → Prop} (l : list T) (Hnil : P nil)
-    (Hind : ∀ (x : T) (l : list T),  P l → P (x::l)) : P l :=
-rec Hnil Hind l
-
 protected theorem cases_on {P : list T → Prop} (l : list T) (Hnil : P nil)
     (Hcons : ∀ (x : T) (l : list T), P (x::l)) : P l :=
 induction_on l Hnil (take x l IH, Hcons x l)
diff --git a/library/data/nat/basic.lean b/library/data/nat/basic.lean
index f26424d946..b314b50967 100644
--- a/library/data/nat/basic.lean
+++ b/library/data/nat/basic.lean
@@ -30,10 +30,6 @@ theorem rec_zero {P : ℕ → Type} (x : P zero) (f : ∀m, P m → P (succ m))
 theorem rec_succ {P : ℕ → Type} (x : P zero) (f : ∀m, P m → P (succ m)) (n : ℕ) :
   nat.rec x f (succ n) = f n (nat.rec x f n)
 
-protected theorem induction_on {P : ℕ → Prop} (a : ℕ) (H1 : P zero) (H2 : ∀ (n : ℕ) (IH : P n), P (succ n)) :
-  P a :=
-nat.rec H1 H2 a
-
 protected definition is_inhabited [instance] : inhabited nat :=
 inhabited.mk zero
 
diff --git a/library/data/num.lean b/library/data/num.lean
index d622ab1ea0..892467214a 100644
--- a/library/data/num.lean
+++ b/library/data/num.lean
@@ -18,10 +18,6 @@ definition pos_num.is_inhabited [instance] : inhabited pos_num :=
 inhabited.mk pos_num.one
 
 namespace pos_num
-  protected theorem induction_on {P : pos_num → Prop} (a : pos_num)
-      (H₁ : P one) (H₂ : ∀ (n : pos_num), P n → P (bit1 n)) (H₃ : ∀ (n : pos_num), P n → P (bit0 n)) : P a :=
-  rec H₁ H₂ H₃ a
-
   definition succ (a : pos_num) : pos_num :=
   rec_on a (bit0 one) (λn r, bit0 r) (λn r, bit1 n)
 
@@ -125,10 +121,6 @@ inhabited.mk num.zero
 
 namespace num
   open pos_num
-  protected theorem induction_on {P : num → Prop} (a : num)
-      (H₁ : P zero) (H₂ : ∀ (p : pos_num), P (pos p)) : P a :=
-  rec H₁ H₂ a
-
   definition succ (a : num) : num :=
   rec_on a (pos one) (λp, pos (succ p))
 
diff --git a/library/data/option.lean b/library/data/option.lean
index 3bbc2f81b2..fe5fb65b4f 100644
--- a/library/data/option.lean
+++ b/library/data/option.lean
@@ -10,10 +10,6 @@ inductive option (A : Type) : Type :=
   some    : A → option A
 
 namespace option
-  protected theorem induction_on {A : Type} {p : option A → Prop} (o : option A)
-    (H1 : p none) (H2 : ∀a, p (some a)) : p o :=
-  rec H1 H2 o
-
   definition is_none {A : Type} (o : option A) : Prop :=
   rec true (λ a, false) o
 
diff --git a/library/data/vector.lean b/library/data/vector.lean
index fbffec6cdd..b72600016f 100644
--- a/library/data/vector.lean
+++ b/library/data/vector.lean
@@ -15,10 +15,6 @@ namespace vector
   section sc_vector
   variable {T : Type}
 
-  protected theorem induction_on {C : ∀ (n : ℕ), vector T n → Prop} {n : ℕ} (v : vector T n) (Hnil : C 0 nil)
-    (Hcons : ∀(x : T) {n : ℕ} (w : vector T n), C n w → C (succ n) (cons x w)) : C n v :=
-  rec_on v Hnil Hcons
-
   protected theorem case_on {C : ∀ (n : ℕ), vector T n → Type} {n : ℕ} (v : vector T n) (Hnil : C 0 nil)
     (Hcons : ∀(x : T) {n : ℕ} (w : vector T n), C (succ n) (cons x w)) : C n v :=
   rec_on v Hnil (take x n v IH, Hcons x v)
diff --git a/library/hott/equiv.lean b/library/hott/equiv.lean
index e76a8ed16b..d0fd633856 100644
--- a/library/hott/equiv.lean
+++ b/library/hott/equiv.lean
@@ -89,7 +89,7 @@ namespace IsEquiv
 
   -- Any function equal to an equivalence is an equivlance as well.
   definition path_closed (Hf : IsEquiv f) (Heq : f ≈ f') : (IsEquiv f') :=
-     path.induction_on Heq Hf
+     path.rec_on Heq Hf
 
   -- Any function pointwise equal to an equivalence is an equivalence as well.
   definition homotopic (Hf : IsEquiv f) (Heq : f ∼ f') : (IsEquiv f') :=
diff --git a/library/hott/path.lean b/library/hott/path.lean
index 8ebef50560..bb6ae51e13 100644
--- a/library/hott/path.lean
+++ b/library/hott/path.lean
@@ -23,10 +23,6 @@ notation a ≈ b := path a b
 notation x ≈ y `:>`:50 A:49 := @path A x y
 definition idp {A : Type} {a : A} := idpath a
 
-protected definition induction_on {A : Type} {a b : A} (p : a ≈ b)
-  {C : Π (b : A) (p : a ≈ b), Type} (H : C a (idpath a)) : C b p :=
-path.rec H p
-
 -- Concatenation and inverse
 -- -------------------------
 
@@ -50,141 +46,141 @@ notation p ⁻¹ := inverse p
 
 -- The identity path is a right unit.
 definition concat_p1 {A : Type} {x y : A} (p : x ≈ y) : p ⬝ idp ≈ p :=
-induction_on p idp
+rec_on p idp
 
 -- The identity path is a right unit.
 definition concat_1p {A : Type} {x y : A} (p : x ≈ y) : idp ⬝ p ≈ p :=
-induction_on p idp
+rec_on p idp
 
 -- Concatenation is associative.
 definition concat_p_pp {A : Type} {x y z t : A} (p : x ≈ y) (q : y ≈ z) (r : z ≈ t) :
   p ⬝ (q ⬝ r) ≈ (p ⬝ q) ⬝ r :=
-induction_on r (induction_on q idp)
+rec_on r (rec_on q idp)
 
 definition concat_pp_p {A : Type} {x y z t : A} (p : x ≈ y) (q : y ≈ z) (r : z ≈ t) :
   (p ⬝ q) ⬝ r ≈ p ⬝ (q ⬝ r) :=
-induction_on r (induction_on q idp)
+rec_on r (rec_on q idp)
 
 -- The left inverse law.
 definition concat_pV {A : Type} {x y : A} (p : x ≈ y) : p ⬝ p⁻¹ ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 -- The right inverse law.
 definition concat_Vp {A : Type} {x y : A} (p : x ≈ y) : p⁻¹ ⬝ p ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 -- Several auxiliary theorems about canceling inverses across associativity. These are somewhat
 -- redundant, following from earlier theorems.
 
 definition concat_V_pp {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : p⁻¹ ⬝ (p ⬝ q) ≈ q :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_p_Vp {A : Type} {x y z : A} (p : x ≈ y) (q : x ≈ z) : p ⬝ (p⁻¹ ⬝ q) ≈ q :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_pp_V {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : (p ⬝ q) ⬝ q⁻¹ ≈ p :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_pV_p {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) : (p ⬝ q⁻¹) ⬝ q ≈ p :=
-induction_on q (take p, induction_on p idp) p
+rec_on q (take p, rec_on p idp) p
 
 -- Inverse distributes over concatenation
 definition inv_pp {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : (p ⬝ q)⁻¹ ≈ q⁻¹ ⬝ p⁻¹ :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition inv_Vp {A : Type} {x y z : A} (p : y ≈ x) (q : y ≈ z) : (p⁻¹ ⬝ q)⁻¹ ≈ q⁻¹ ⬝ p :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 -- universe metavariables
 definition inv_pV {A : Type} {x y z : A} (p : x ≈ y) (q : z ≈ y) : (p ⬝ q⁻¹)⁻¹ ≈ q ⬝ p⁻¹ :=
-induction_on p (take q, induction_on q idp) q
+rec_on p (take q, rec_on q idp) q
 
 definition inv_VV {A : Type} {x y z : A} (p : y ≈ x) (q : z ≈ y) : (p⁻¹ ⬝ q⁻¹)⁻¹ ≈ q ⬝ p :=
-induction_on p (induction_on q idp)
+rec_on p (rec_on q idp)
 
 -- Inverse is an involution.
 definition inv_V {A : Type} {x y : A} (p : x ≈ y) : p⁻¹⁻¹ ≈ p :=
-induction_on p idp
+rec_on p idp
 
 -- Theorems for moving things around in equations
 -- ----------------------------------------------
 
 definition moveR_Mp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   p ≈ (r⁻¹ ⬝ q) → (r ⬝ p) ≈ q :=
-induction_on r (take p h, concat_1p _ ⬝ h ⬝ concat_1p _) p
+rec_on r (take p h, concat_1p _ ⬝ h ⬝ concat_1p _) p
 
 definition moveR_pM {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   r ≈ q ⬝ p⁻¹ → r ⬝ p ≈ q :=
-induction_on p (take q h, (concat_p1 _ ⬝ h ⬝ concat_p1 _)) q
+rec_on p (take q h, (concat_p1 _ ⬝ h ⬝ concat_p1 _)) q
 
 definition moveR_Vp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : x ≈ y) :
   p ≈ r ⬝ q → r⁻¹ ⬝ p ≈ q :=
-induction_on r (take q h, concat_1p _ ⬝ h ⬝ concat_1p _) q
+rec_on r (take q h, concat_1p _ ⬝ h ⬝ concat_1p _) q
 
 definition moveR_pV {A : Type} {x y z : A} (p : z ≈ x) (q : y ≈ z) (r : y ≈ x) :
   r ≈ q ⬝ p → r ⬝ p⁻¹ ≈ q :=
-induction_on p (take r h, concat_p1 _ ⬝ h ⬝ concat_p1 _) r
+rec_on p (take r h, concat_p1 _ ⬝ h ⬝ concat_p1 _) r
 
 definition moveL_Mp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   r⁻¹ ⬝ q ≈ p → q ≈ r ⬝ p :=
-induction_on r (take p h, (concat_1p _)⁻¹ ⬝ h ⬝ (concat_1p _)⁻¹) p
+rec_on r (take p h, (concat_1p _)⁻¹ ⬝ h ⬝ (concat_1p _)⁻¹) p
 
 definition moveL_pM {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   q ⬝ p⁻¹ ≈ r → q ≈ r ⬝ p :=
-induction_on p (take q h, (concat_p1 _)⁻¹ ⬝ h ⬝ (concat_p1 _)⁻¹) q
+rec_on p (take q h, (concat_p1 _)⁻¹ ⬝ h ⬝ (concat_p1 _)⁻¹) q
 
 definition moveL_Vp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : x ≈ y) :
   r ⬝ q ≈ p → q ≈ r⁻¹ ⬝ p :=
-induction_on r (take q h, (concat_1p _)⁻¹ ⬝ h ⬝ (concat_1p _)⁻¹) q
+rec_on r (take q h, (concat_1p _)⁻¹ ⬝ h ⬝ (concat_1p _)⁻¹) q
 
 definition moveL_pV {A : Type} {x y z : A} (p : z ≈ x) (q : y ≈ z) (r : y ≈ x) :
   q ⬝ p ≈ r → q ≈ r ⬝ p⁻¹ :=
-induction_on p (take r h, (concat_p1 _)⁻¹ ⬝ h ⬝ (concat_p1 _)⁻¹) r
+rec_on p (take r h, (concat_p1 _)⁻¹ ⬝ h ⬝ (concat_p1 _)⁻¹) r
 
 definition moveL_1M {A : Type} {x y : A} (p q : x ≈ y) :
   p ⬝ q⁻¹ ≈ idp → p ≈ q :=
-induction_on q (take p h, (concat_p1 _)⁻¹ ⬝ h) p
+rec_on q (take p h, (concat_p1 _)⁻¹ ⬝ h) p
 
 definition moveL_M1 {A : Type} {x y : A} (p q : x ≈ y) :
   q⁻¹ ⬝ p ≈ idp → p ≈ q :=
-induction_on q (take p h, (concat_1p _)⁻¹ ⬝ h) p
+rec_on q (take p h, (concat_1p _)⁻¹ ⬝ h) p
 
 definition moveL_1V {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   p ⬝ q ≈ idp → p ≈ q⁻¹ :=
-induction_on q (take p h, (concat_p1 _)⁻¹ ⬝ h) p
+rec_on q (take p h, (concat_p1 _)⁻¹ ⬝ h) p
 
 definition moveL_V1 {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   q ⬝ p ≈ idp → p ≈ q⁻¹ :=
-induction_on q (take p h, (concat_1p _)⁻¹ ⬝ h) p
+rec_on q (take p h, (concat_1p _)⁻¹ ⬝ h) p
 
 definition moveR_M1 {A : Type} {x y : A} (p q : x ≈ y) :
   idp ≈ p⁻¹ ⬝ q → p ≈ q :=
-induction_on p (take q h, h ⬝ (concat_1p _)) q
+rec_on p (take q h, h ⬝ (concat_1p _)) q
 
 definition moveR_1M {A : Type} {x y : A} (p q : x ≈ y) :
   idp ≈ q ⬝ p⁻¹ → p ≈ q :=
-induction_on p (take q h, h ⬝ (concat_p1 _)) q
+rec_on p (take q h, h ⬝ (concat_p1 _)) q
 
 definition moveR_1V {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   idp ≈ q ⬝ p → p⁻¹ ≈ q :=
-induction_on p (take q h, h ⬝ (concat_p1 _)) q
+rec_on p (take q h, h ⬝ (concat_p1 _)) q
 
 definition moveR_V1 {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   idp ≈ p ⬝ q → p⁻¹ ≈ q :=
-induction_on p (take q h, h ⬝ (concat_1p _)) q
+rec_on p (take q h, h ⬝ (concat_1p _)) q
 
 
 -- Transport
 -- ---------
 
 definition transport {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) : P y :=
-path.induction_on p u
+path.rec_on p u
 
 -- This idiom makes the operation right associative.
 notation p `▹`:65 x:64 := transport _ p x
 
 definition ap ⦃A B : Type⦄ (f : A → B) {x y:A} (p : x ≈ y) : f x ≈ f y :=
-path.induction_on p idp
+path.rec_on p idp
 
 definition ap01 := ap
 
@@ -194,15 +190,15 @@ definition pointwise_paths {A : Type} {P : A → Type} (f g : Πx, P x) : Type :
 notation f ∼ g := pointwise_paths f g
 
 definition apD10 {A} {B : A → Type} {f g : Πx, B x} (H : f ≈ g) : f ∼ g :=
-λx, path.induction_on H idp
+λx, path.rec_on H idp
 
 definition ap10 {A B} {f g : A → B} (H : f ≈ g) : f ∼ g := apD10 H
 
 definition ap11 {A B} {f g : A → B} (H : f ≈ g) {x y : A} (p : x ≈ y) : f x ≈ g y :=
-induction_on H (induction_on p idp)
+rec_on H (rec_on p idp)
 
 definition apD {A:Type} {B : A → Type} (f : Πa:A, B a) {x y : A} (p : x ≈ y) : p ▹ (f x) ≈ f y :=
-induction_on p idp
+rec_on p idp
 
 
 -- calc enviroment
@@ -218,19 +214,19 @@ calc_refl idpath
 
 definition moveR_transport_p {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) (v : P y) :
   u ≈ p⁻¹ ▹ v → p ▹ u ≈ v :=
-induction_on p (take v, id) v
+rec_on p (take v, id) v
 
 definition moveR_transport_V {A : Type} (P : A → Type) {x y : A} (p : y ≈ x) (u : P x) (v : P y) :
   u ≈ p ▹ v → p⁻¹ ▹ u ≈ v :=
-induction_on p (take u, id) u
+rec_on p (take u, id) u
 
 definition moveL_transport_V {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) (v : P y) :
   p ▹ u ≈ v → u ≈ p⁻¹ ▹ v :=
-induction_on p (take v, id) v
+rec_on p (take v, id) v
 
 definition moveL_transport_p {A : Type} (P : A → Type) {x y : A} (p : y ≈ x) (u : P x) (v : P y) :
   p⁻¹ ▹ u ≈ v → u ≈ p ▹ v :=
-induction_on p (take u, id) u
+rec_on p (take u, id) u
 
 -- Functoriality of functions
 -- --------------------------
@@ -246,109 +242,109 @@ definition apD_1 {A B} (x : A) (f : Π x : A, B x) : apD f idp ≈ idp :> (f x 
 -- Functions commute with concatenation.
 definition ap_pp {A B : Type} (f : A → B) {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   ap f (p ⬝ q) ≈ (ap f p) ⬝ (ap f q) :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition ap_p_pp {A B : Type} (f : A → B) {w x y z : A} (r : f w ≈ f x) (p : x ≈ y) (q : y ≈ z) :
   r ⬝ (ap f (p ⬝ q)) ≈ (r ⬝ ap f p) ⬝ (ap f q) :=
-induction_on q (take p, induction_on p (concat_p_pp r idp idp)) p
+rec_on q (take p, rec_on p (concat_p_pp r idp idp)) p
 
 definition ap_pp_p {A B : Type} (f : A → B) {w x y z : A} (p : x ≈ y) (q : y ≈ z) (r : f z ≈ f w) :
   (ap f (p ⬝ q)) ⬝ r ≈ (ap f p) ⬝ (ap f q ⬝ r) :=
-induction_on q (induction_on p (take r, concat_pp_p _ _ _)) r
+rec_on q (rec_on p (take r, concat_pp_p _ _ _)) r
 
 -- Functions commute with path inverses.
 definition inverse_ap {A B : Type} (f : A → B) {x y : A} (p : x ≈ y) : (ap f p)⁻¹ ≈ ap f (p⁻¹) :=
-induction_on p idp
+rec_on p idp
 
 definition ap_V {A B : Type} (f : A → B) {x y : A} (p : x ≈ y) : ap f (p⁻¹) ≈ (ap f p)⁻¹ :=
-induction_on p idp
+rec_on p idp
 
 -- [ap] itself is functorial in the first argument.
 
 definition ap_idmap {A : Type} {x y : A} (p : x ≈ y) : ap id p ≈ p :=
-induction_on p idp
+rec_on p idp
 
 definition ap_compose {A B C : Type} (f : A → B) (g : B → C) {x y : A} (p : x ≈ y) :
   ap (g ∘ f) p ≈ ap g (ap f p) :=
-induction_on p idp
+rec_on p idp
 
 -- Sometimes we don't have the actual function [compose].
 definition ap_compose' {A B C : Type} (f : A → B) (g : B → C) {x y : A} (p : x ≈ y) :
   ap (λa, g (f a)) p ≈ ap g (ap f p) :=
-induction_on p idp
+rec_on p idp
 
 -- The action of constant maps.
 definition ap_const {A B : Type} {x y : A} (p : x ≈ y) (z : B) :
   ap (λu, z) p ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 -- Naturality of [ap].
 definition concat_Ap {A B : Type} {f g : A → B} (p : Π x, f x ≈ g x) {x y : A} (q : x ≈ y) :
   (ap f q) ⬝ (p y) ≈ (p x) ⬝ (ap g q) :=
-induction_on q (concat_1p _ ⬝ (concat_p1 _)⁻¹)
+rec_on q (concat_1p _ ⬝ (concat_p1 _)⁻¹)
 
 -- Naturality of [ap] at identity.
 definition concat_A1p {A : Type} {f : A → A} (p : Πx, f x ≈ x) {x y : A} (q : x ≈ y) :
   (ap f q) ⬝ (p y) ≈ (p x) ⬝ q :=
-induction_on q (concat_1p _ ⬝ (concat_p1 _)⁻¹)
+rec_on q (concat_1p _ ⬝ (concat_p1 _)⁻¹)
 
 definition concat_pA1 {A : Type} {f : A → A} (p : Πx, x ≈ f x) {x y : A} (q : x ≈ y) :
   (p x) ⬝ (ap f q) ≈  q ⬝ (p y) :=
-induction_on q (concat_p1 _ ⬝ (concat_1p _)⁻¹)
+rec_on q (concat_p1 _ ⬝ (concat_1p _)⁻¹)
 
 -- Naturality with other paths hanging around.
 
 definition concat_pA_pp {A B : Type} {f g : A → B} (p : Πx, f x ≈ g x) {x y : A} (q : x ≈ y)
     {w z : B} (r : w ≈ f x) (s : g y ≈ z) :
   (r ⬝ ap f q) ⬝ (p y ⬝ s) ≈ (r ⬝ p x) ⬝ (ap g q ⬝ s) :=
-induction_on s (induction_on q idp)
+rec_on s (rec_on q idp)
 
 definition concat_pA_p {A B : Type} {f g : A → B} (p : Πx, f x ≈ g x) {x y : A} (q : x ≈ y)
     {w : B} (r : w ≈ f x) :
   (r ⬝ ap f q) ⬝ p y ≈ (r ⬝ p x) ⬝ ap g q :=
-induction_on q idp
+rec_on q idp
 
 -- TODO: try this using the simplifier, and compare proofs
 definition concat_A_pp {A B : Type} {f g : A → B} (p : Πx, f x ≈ g x) {x y : A} (q : x ≈ y)
     {z : B} (s : g y ≈ z) :
   (ap f q) ⬝ (p y ⬝ s) ≈ (p x) ⬝ (ap g q ⬝ s) :=
-induction_on s (induction_on q
+rec_on s (rec_on q
   (calc
     (ap f idp) ⬝ (p x ⬝ idp) ≈ idp ⬝ p x : idp
       ... ≈ p x : concat_1p _
       ... ≈ (p x) ⬝ (ap g idp ⬝ idp) : idp))
 -- This also works:
--- induction_on s (induction_on q (concat_1p _ ▹ idp))
+-- rec_on s (rec_on q (concat_1p _ ▹ idp))
 
 definition concat_pA1_pp {A : Type} {f : A → A} (p : Πx, f x ≈ x) {x y : A} (q : x ≈ y)
     {w z : A} (r : w ≈ f x) (s : y ≈ z) :
   (r ⬝ ap f q) ⬝ (p y ⬝ s) ≈ (r ⬝ p x) ⬝ (q ⬝ s) :=
-induction_on s (induction_on q idp)
+rec_on s (rec_on q idp)
 
 definition concat_pp_A1p {A : Type} {g : A → A} (p : Πx, x ≈ g x) {x y : A} (q : x ≈ y)
     {w z : A} (r : w ≈ x) (s : g y ≈ z) :
   (r ⬝ p x) ⬝ (ap g q ⬝ s) ≈ (r ⬝ q) ⬝ (p y ⬝ s) :=
-induction_on s (induction_on q idp)
+rec_on s (rec_on q idp)
 
 definition concat_pA1_p {A : Type} {f : A → A} (p : Πx, f x ≈ x) {x y : A} (q : x ≈ y)
     {w : A} (r : w ≈ f x) :
   (r ⬝ ap f q) ⬝ p y ≈ (r ⬝ p x) ⬝ q :=
-induction_on q idp
+rec_on q idp
 
 definition concat_A1_pp {A : Type} {f : A → A} (p : Πx, f x ≈ x) {x y : A} (q : x ≈ y)
     {z : A} (s : y ≈ z) :
   (ap f q) ⬝ (p y ⬝ s) ≈ (p x) ⬝ (q ⬝ s) :=
-induction_on s (induction_on q (concat_1p _ ▹ idp))
+rec_on s (rec_on q (concat_1p _ ▹ idp))
 
 definition concat_pp_A1 {A : Type} {g : A → A} (p : Πx, x ≈ g x) {x y : A} (q : x ≈ y)
     {w : A} (r : w ≈ x) :
   (r ⬝ p x) ⬝ ap g q ≈ (r ⬝ q) ⬝ p y :=
-induction_on q idp
+rec_on q idp
 
 definition concat_p_A1p {A : Type} {g : A → A} (p : Πx, x ≈ g x) {x y : A} (q : x ≈ y)
     {z : A} (s : g y ≈ z) :
   p x ⬝ (ap g q ⬝ s) ≈ q ⬝ (p y ⬝ s) :=
-induction_on s (induction_on q (concat_1p _ ▹ idp))
+rec_on s (rec_on q (concat_1p _ ▹ idp))
 
 
 -- Action of [apD10] and [ap10] on paths
@@ -360,11 +356,11 @@ definition apD10_1 {A} {B : A → Type} (f : Πx, B x) (x : A) : apD10 (idpath f
 
 definition apD10_pp {A} {B : A → Type} {f f' f'' : Πx, B x} (h : f ≈ f') (h' : f' ≈ f'') (x : A) :
   apD10 (h ⬝ h') x ≈ apD10 h x ⬝ apD10 h' x :=
-induction_on h (take h', induction_on h' idp) h'
+rec_on h (take h', rec_on h' idp) h'
 
 definition apD10_V {A : Type} {B : A → Type} {f g : Πx : A, B x} (h : f ≈ g) (x : A) :
   apD10 (h⁻¹) x ≈ (apD10 h x)⁻¹ :=
-induction_on h idp
+rec_on h idp
 
 definition ap10_1 {A B} {f : A → B} (x : A) : ap10 (idpath f) x ≈ idp := idp
 
@@ -376,7 +372,7 @@ definition ap10_V {A B} {f g : A→B} (h : f ≈ g) (x:A) : ap10 (h⁻¹) x ≈
 -- [ap10] also behaves nicely on paths produced by [ap]
 definition ap_ap10 {A B C} (f g : A → B) (h : B → C) (p : f ≈ g) (a : A) :
   ap h (ap10 p a) ≈ ap10 (ap (λ f', h ∘ f') p) a:=
-induction_on p idp
+rec_on p idp
 
 
 -- Transport and the groupoid structure of paths
@@ -387,7 +383,7 @@ definition transport_1 {A : Type} (P : A → Type) {x : A} (u : P x) :
 
 definition transport_pp {A : Type} (P : A → Type) {x y z : A} (p : x ≈ y) (q : y ≈ z) (u : P x) :
   p ⬝ q ▹ u ≈ q ▹ p ▹ u :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition transport_pV {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (z : P y) :
   p ▹ p⁻¹ ▹ z ≈ z :=
@@ -403,18 +399,18 @@ definition transport_p_pp {A : Type} (P : A → Type)
       ap (transport P r) (transport_pp P p q u)
     ≈ (transport_pp P p (q ⬝ r) u) ⬝ (transport_pp P q r (p ▹ u))
     :> ((p ⬝ (q ⬝ r)) ▹ u ≈ r ▹ q ▹ p ▹ u) :=
-induction_on r (induction_on q (induction_on p idp))
+rec_on r (rec_on q (rec_on p idp))
 
 --  Here is another coherence lemma for transport.
 definition transport_pVp {A} (P : A → Type) {x y : A} (p : x ≈ y) (z : P x) :
   transport_pV P p (transport P p z) ≈ ap (transport P p) (transport_Vp P p z) :=
-induction_on p idp
+rec_on p idp
 
 -- Dependent transport in a doubly dependent type.
 definition transportD {A : Type} (B : A → Type) (C : Π a : A, B a → Type)
     {x1 x2 : A} (p : x1 ≈ x2) (y : B x1) (z : C x1 y) :
   C x2 (p ▹ y) :=
-induction_on p z
+rec_on p z
 
 -- Transporting along higher-dimensional paths
 definition transport2 {A : Type} (P : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q) (z : P x) :
@@ -425,26 +421,26 @@ ap (λp', p' ▹ z) r
 definition transport2_is_ap10 {A : Type} (Q : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q)
     (z : Q x) :
   transport2 Q r z ≈ ap10 (ap (transport Q) r) z :=
-induction_on r idp
+rec_on r idp
 
 definition transport2_p2p {A : Type} (P : A → Type) {x y : A} {p1 p2 p3 : x ≈ y}
     (r1 : p1 ≈ p2) (r2 : p2 ≈ p3) (z : P x) :
   transport2 P (r1 ⬝ r2) z ≈ transport2 P r1 z ⬝ transport2 P r2 z :=
-induction_on r1 (induction_on r2 idp)
+rec_on r1 (rec_on r2 idp)
 
 definition transport2_V {A : Type} (Q : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q) (z : Q x) :
   transport2 Q (r⁻¹) z ≈ ((transport2 Q r z)⁻¹) :=
-induction_on r idp
+rec_on r idp
 
 definition concat_AT {A : Type} (P : A → Type) {x y : A} {p q : x ≈ y} {z w : P x} (r : p ≈ q)
     (s : z ≈ w) :
   ap (transport P p) s  ⬝  transport2 P r w ≈ transport2 P r z  ⬝  ap (transport P q) s :=
-induction_on r (concat_p1 _ ⬝ (concat_1p _)⁻¹)
+rec_on r (concat_p1 _ ⬝ (concat_1p _)⁻¹)
 
 -- TODO (from Coq library): What should this be called?
 definition ap_transport {A} {P Q : A → Type} {x y : A} (p : x ≈ y) (f : Πx, P x → Q x) (z : P x) :
   f y (p ▹ z) ≈ (p ▹ (f x z)) :=
-induction_on p idp
+rec_on p idp
 
 
 -- Transporting in particular fibrations
@@ -462,33 +458,33 @@ subdirectory.  Here we consider only the most basic cases.
 -- Transporting in a constant fibration.
 definition transport_const {A B : Type} {x1 x2 : A} (p : x1 ≈ x2) (y : B) :
   transport (λx, B) p y ≈ y :=
-induction_on p idp
+rec_on p idp
 
 definition transport2_const {A B : Type} {x1 x2 : A} {p q : x1 ≈ x2} (r : p ≈ q) (y : B) :
   transport_const p y ≈ transport2 (λu, B) r y ⬝ transport_const q y :=
-induction_on r (concat_1p _)⁻¹
+rec_on r (concat_1p _)⁻¹
 
 -- Transporting in a pulled back fibration.
 definition transport_compose {A B} {x y : A} (P : B → Type) (f : A → B) (p : x ≈ y) (z : P (f x)) :
   transport (λx, P (f x)) p z  ≈  transport P (ap f p) z :=
-induction_on p idp
+rec_on p idp
 
 definition transport_precompose {A B C} (f : A → B) (g g' : B → C) (p : g ≈ g') :
   transport (λh : B → C, g ∘ f ≈ h ∘ f) p idp ≈ ap (λh, h ∘ f) p :=
-induction_on p idp
+rec_on p idp
 
 definition apD10_ap_precompose {A B C} (f : A → B) (g g' : B → C) (p : g ≈ g') (a : A) :
   apD10 (ap (λh : B → C, h ∘ f) p) a ≈ apD10 p (f a) :=
-induction_on p idp
+rec_on p idp
 
 definition apD10_ap_postcompose {A B C} (f : B → C) (g g' : A → B) (p : g ≈ g') (a : A) :
   apD10 (ap (λh : A → B, f ∘ h) p) a ≈ ap f (apD10 p a) :=
-induction_on p idp
+rec_on p idp
 
 -- A special case of [transport_compose] which seems to come up a lot.
 definition transport_idmap_ap A (P : A → Type) x y (p : x ≈ y) (u : P x) :
   transport P p u ≈ transport (λz, z) (ap P p) u :=
-induction_on p idp
+rec_on p idp
 
 
 -- The behavior of [ap] and [apD]
@@ -497,7 +493,7 @@ induction_on p idp
 -- In a constant fibration, [apD] reduces to [ap], modulo [transport_const].
 definition apD_const {A B} {x y : A} (f : A → B) (p: x ≈ y) :
   apD f p ≈ transport_const p (f x) ⬝ ap f p :=
-induction_on p idp
+rec_on p idp
 
 
 -- The 2-dimensional groupoid structure
@@ -506,13 +502,13 @@ induction_on p idp
 -- Horizontal composition of 2-dimensional paths.
 definition concat2 {A} {x y z : A} {p p' : x ≈ y} {q q' : y ≈ z} (h : p ≈ p') (h' : q ≈ q') :
   p ⬝ q ≈ p' ⬝ q' :=
-induction_on h (induction_on h' idp)
+rec_on h (rec_on h' idp)
 
 infixl `◾`:75 := concat2
 
 -- 2-dimensional path inversion
 definition inverse2 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) : p⁻¹ ≈ q⁻¹ :=
-induction_on h idp
+rec_on h idp
 
 
 -- Whiskering
@@ -527,47 +523,47 @@ h ◾ idp
 -- Unwhiskering, a.k.a. cancelling
 
 definition cancelL {A} {x y z : A} (p : x ≈ y) (q r : y ≈ z) : (p ⬝ q ≈ p ⬝ r) → (q ≈ r) :=
-induction_on p (take r, induction_on r (take q a, (concat_1p q)⁻¹ ⬝ a)) r q
+rec_on p (take r, rec_on r (take q a, (concat_1p q)⁻¹ ⬝ a)) r q
 
 definition cancelR {A} {x y z : A} (p q : x ≈ y) (r : y ≈ z) : (p ⬝ r ≈ q ⬝ r) → (p ≈ q) :=
-induction_on r (induction_on p (take q a, a ⬝ concat_p1 q)) q
+rec_on r (rec_on p (take q a, a ⬝ concat_p1 q)) q
 
 -- Whiskering and identity paths.
 
 definition whiskerR_p1 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   (concat_p1 p)⁻¹ ⬝ whiskerR h idp ⬝ concat_p1 q ≈ h :=
-induction_on h (induction_on p idp)
+rec_on h (rec_on p idp)
 
 definition whiskerR_1p {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   whiskerR idp q ≈ idp :> (p ⬝ q ≈ p ⬝ q) :=
-induction_on q idp
+rec_on q idp
 
 definition whiskerL_p1 {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   whiskerL p idp ≈ idp :> (p ⬝ q ≈ p ⬝ q) :=
-induction_on q idp
+rec_on q idp
 
 definition whiskerL_1p {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   (concat_1p p) ⁻¹ ⬝ whiskerL idp h ⬝ concat_1p q ≈ h :=
-induction_on h (induction_on p idp)
+rec_on h (rec_on p idp)
 
 definition concat2_p1 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   h ◾ idp ≈ whiskerR h idp :> (p ⬝ idp ≈ q ⬝ idp) :=
-induction_on h idp
+rec_on h idp
 
 definition concat2_1p {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   idp ◾ h ≈ whiskerL idp h :> (idp ⬝ p ≈ idp ⬝ q) :=
-induction_on h idp
+rec_on h idp
 
 -- TODO: note, 4 inductions
 -- The interchange law for concatenation.
 definition concat_concat2 {A : Type} {x y z : A} {p p' p'' : x ≈ y} {q q' q'' : y ≈ z}
     (a : p ≈ p') (b : p' ≈ p'') (c : q ≈ q') (d : q' ≈ q'') :
   (a ◾ c) ⬝ (b ◾ d) ≈ (a ⬝ b) ◾ (c ⬝ d) :=
-induction_on d (induction_on c (induction_on b (induction_on a idp)))
+rec_on d (rec_on c (rec_on b (rec_on a idp)))
 
 definition concat_whisker {A} {x y z : A} (p p' : x ≈ y) (q q' : y ≈ z) (a : p ≈ p') (b : q ≈ q') :
   (whiskerR a q) ⬝ (whiskerL p' b) ≈ (whiskerL p b) ⬝ (whiskerR a q') :=
-induction_on b (induction_on a (concat_1p _)⁻¹)
+rec_on b (rec_on a (concat_1p _)⁻¹)
 
 -- Structure corresponding to the coherence equations of a bicategory.
 
@@ -577,12 +573,12 @@ definition pentagon {A : Type} {v w x y z : A} (p : v ≈ w) (q : w ≈ x) (r :
     ⬝ concat_p_pp p (q ⬝ r) s
     ⬝ whiskerR (concat_p_pp p q r) s
   ≈ concat_p_pp p q (r ⬝ s) ⬝ concat_p_pp (p ⬝ q) r s :=
-induction_on s (induction_on r (induction_on q (induction_on p idp)))
+rec_on s (rec_on r (rec_on q (rec_on p idp)))
 
 -- The 3-cell witnessing the left unit triangle.
 definition triangulator {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   concat_p_pp p idp q ⬝ whiskerR (concat_p1 p) q ≈ whiskerL p (concat_1p q) :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition eckmann_hilton {A : Type} {x:A} (p q : idp ≈ idp :> (x ≈ x)) : p ⬝ q ≈ q ⬝ p :=
   (!whiskerR_p1 ◾ !whiskerL_1p)⁻¹
@@ -595,24 +591,24 @@ definition eckmann_hilton {A : Type} {x:A} (p q : idp ≈ idp :> (x ≈ x)) : p
 
 -- The action of functions on 2-dimensional paths
 definition ap02 {A B : Type} (f:A → B) {x y : A} {p q : x ≈ y} (r : p ≈ q) : ap f p ≈ ap f q :=
-induction_on r idp
+rec_on r idp
 
 definition ap02_pp {A B} (f : A → B) {x y : A} {p p' p'' : x ≈ y} (r : p ≈ p') (r' : p' ≈ p'') :
   ap02 f (r ⬝ r') ≈ ap02 f r ⬝ ap02 f r' :=
-induction_on r (induction_on r' idp)
+rec_on r (rec_on r' idp)
 
 definition ap02_p2p {A B} (f : A → B) {x y z : A} {p p' : x ≈ y} {q q' :y ≈ z} (r : p ≈ p')
     (s : q ≈ q') :
   ap02 f (r ◾ s) ≈   ap_pp f p q
                       ⬝ (ap02 f r  ◾  ap02 f s)
                       ⬝ (ap_pp f p' q')⁻¹ :=
-induction_on r (induction_on s (induction_on q (induction_on p idp)))
+rec_on r (rec_on s (rec_on q (rec_on p idp)))
 
--- induction_on r (induction_on s (induction_on p (induction_on q idp)))
+-- rec_on r (rec_on s (rec_on p (rec_on q idp)))
 
 definition apD02 {A : Type} {B : A → Type} {x y : A} {p q : x ≈ y} (f : Π x, B x) (r : p ≈ q) :
   apD f p ≈ transport2 B r (f x) ⬝ apD f q :=
-induction_on r (concat_1p _)⁻¹
+rec_on r (concat_1p _)⁻¹
 
 -- And now for a lemma whose statement is much longer than its proof.
 definition apD02_pp {A} (B : A → Type) (f : Π x:A, B x) {x y : A}
@@ -621,7 +617,7 @@ definition apD02_pp {A} (B : A → Type) (f : Π x:A, B x) {x y : A}
     ⬝ whiskerL (transport2 B r1 (f x)) (apD02 f r2)
     ⬝ concat_p_pp _ _ _
     ⬝ (whiskerR ((transport2_p2p B r1 r2 (f x))⁻¹) (apD f p3)) :=
-induction_on r2 (induction_on r1 (induction_on p1 idp))
+rec_on r2 (rec_on r1 (rec_on p1 idp))
 
 /- From the Coq version:
 
diff --git a/library/logic/decidable.lean b/library/logic/decidable.lean
index e8ca1d09be..70ce13ad93 100644
--- a/library/logic/decidable.lean
+++ b/library/logic/decidable.lean
@@ -16,8 +16,6 @@ namespace decidable
   inr not_false_trivial
 
   variables {p q : Prop}
-  protected theorem induction_on {C : Prop} (H : decidable p) (H1 : p → C) (H2 : ¬p → C) : C :=
-  decidable.rec H1 H2 H
 
   definition rec_on_true [H : decidable p] {H1 : p → Type} {H2 : ¬p → Type} (H3 : p) (H4 : H1 H3)
       : rec_on H H1 H2 :=
diff --git a/src/frontends/lean/inductive_cmd.cpp b/src/frontends/lean/inductive_cmd.cpp
index 92d4fcc2f6..ab50f1f8e3 100644
--- a/src/frontends/lean/inductive_cmd.cpp
+++ b/src/frontends/lean/inductive_cmd.cpp
@@ -22,6 +22,7 @@ Author: Leonardo de Moura
 #include "library/explicit.h"
 #include "library/reducible.h"
 #include "library/definitional/rec_on.h"
+#include "library/definitional/induction_on.h"
 #include "frontends/lean/decl_cmds.h"
 #include "frontends/lean/util.h"
 #include "frontends/lean/class.h"
@@ -650,6 +651,7 @@ struct inductive_cmd_fn {
     environment mk_aux_decls(environment env, buffer<inductive_decl> const & decls) {
         for (inductive_decl const & d : decls) {
             env = mk_rec_on(env, inductive_decl_name(d));
+            env = mk_induction_on(env, inductive_decl_name(d));
         }
         return env;
     }
diff --git a/src/library/definitional/CMakeLists.txt b/src/library/definitional/CMakeLists.txt
index a4812be79c..4716f9a51a 100644
--- a/src/library/definitional/CMakeLists.txt
+++ b/src/library/definitional/CMakeLists.txt
@@ -1,3 +1,3 @@
-add_library(definitional rec_on.cpp)
+add_library(definitional rec_on.cpp induction_on.cpp)
 
 target_link_libraries(definitional ${LEAN_LIBS})
diff --git a/src/library/definitional/induction_on.cpp b/src/library/definitional/induction_on.cpp
new file mode 100644
index 0000000000..971bff19e4
--- /dev/null
+++ b/src/library/definitional/induction_on.cpp
@@ -0,0 +1,48 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#include "kernel/environment.h"
+#include "kernel/instantiate.h"
+#include "kernel/type_checker.h"
+#include "library/module.h"
+#include "library/protected.h"
+
+namespace lean {
+environment mk_induction_on(environment const & env, name const & n) {
+    if (!env.impredicative())
+        throw exception("induction_on generation failed, Prop/Type.{0} is not impredicative in the given environment");
+    name rec_on_name(n, "rec_on");
+    name induction_on_name(n, "induction_on");
+    name_generator ngen;
+    declaration rec_on_decl   = env.get(rec_on_name);
+    declaration ind_decl      = env.get(n);
+    unsigned rec_on_num_univs = length(rec_on_decl.get_univ_params());
+    unsigned ind_num_univs    = length(ind_decl.get_univ_params());
+    bool opaque               = false;
+    bool use_conv_opt         = true;
+    environment new_env       = env;
+    if (rec_on_num_univs == ind_num_univs) {
+        // easy case, induction_on is just an alias for rec_on
+        certified_declaration cdecl = check(new_env,
+                                            mk_definition(new_env, induction_on_name, rec_on_decl.get_univ_params(),
+                                                          rec_on_decl.get_type(), rec_on_decl.get_value(),
+                                                          opaque, rec_on_decl.get_module_idx(), use_conv_opt));
+        new_env = module::add(new_env, cdecl);
+    } else {
+        level_param_names induction_on_univs = tail(rec_on_decl.get_univ_params());
+        level_param_names from = to_list(head(rec_on_decl.get_univ_params()));
+        levels            to   = to_list(mk_level_zero());
+        expr induction_on_type  = instantiate_univ_params(rec_on_decl.get_type(), from, to);
+        expr induction_on_value = instantiate_univ_params(rec_on_decl.get_value(), from, to);
+        certified_declaration cdecl = check(new_env,
+                                            mk_definition(new_env, induction_on_name, induction_on_univs,
+                                                          induction_on_type, induction_on_value,
+                                                          opaque, rec_on_decl.get_module_idx(), use_conv_opt));
+        new_env = module::add(new_env, cdecl);
+    }
+    return add_protected(new_env, induction_on_name);
+}
+}
diff --git a/src/library/definitional/induction_on.h b/src/library/definitional/induction_on.h
new file mode 100644
index 0000000000..e67881ebd2
--- /dev/null
+++ b/src/library/definitional/induction_on.h
@@ -0,0 +1,19 @@
+/*
+Copyright (c) 2014 Microsoft Corporation. All rights reserved.
+Released under Apache 2.0 license as described in the file LICENSE.
+
+Author: Leonardo de Moura
+*/
+#pragma once
+#include "kernel/environment.h"
+
+namespace lean {
+/** \brief Given an inductive datatype \c n in \c env, add
+    <tt>n.induction_on</tt> to the environment.
+
+    \remark Throws an exception if \c n is not an inductive datatype.
+
+    \remark Throws an exception if <tt>n.rec_on</tt> is not defined in the given environment.
+*/
+environment mk_induction_on(environment const & env, name const & n);
+}
diff --git a/src/library/definitional/rec_on.h b/src/library/definitional/rec_on.h
index b89c8a21d9..82d3b46a04 100644
--- a/src/library/definitional/rec_on.h
+++ b/src/library/definitional/rec_on.h
@@ -12,6 +12,8 @@ namespace lean {
     <tt>n.rec_on</tt> to the environment.
 
     \remark <tt>rec_on</tt> is based on <tt>n.rec</tt>
+
+    \remark Throws an exception if \c n is not an inductive datatype.
 */
 environment mk_rec_on(environment const & env, name const & n);
 }
diff --git a/tests/lean/interactive/findp.input.expected.out b/tests/lean/interactive/findp.input.expected.out
index b67b0723f9..a54e11f1bc 100644
--- a/tests/lean/interactive/findp.input.expected.out
+++ b/tests/lean/interactive/findp.input.expected.out
@@ -5,6 +5,7 @@ false|Prop
 false.rec|∀ (C : Prop), false → C
 false_elim|false → ?c
 false.rec_on|∀ (C : Prop), false → C
+false.induction_on|∀ (C : Prop), false → C
 not_false_trivial|¬ false
 true_ne_false|¬ true = false
 p_ne_false|?p → ?p ≠ false
diff --git a/tests/lean/interactive/num2.input.expected.out b/tests/lean/interactive/num2.input.expected.out
index 32e22f7408..9f4c2df679 100644
--- a/tests/lean/interactive/num2.input.expected.out
+++ b/tests/lean/interactive/num2.input.expected.out
@@ -6,6 +6,7 @@
 pos_num.bit0|pos_num → pos_num
 pos_num.is_inhabited|inhabited pos_num
 pos_num.inc|pos_num → pos_num
+pos_num.induction_on|Π (n : pos_num), ?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → ?C n
 pos_num.bit1|pos_num → pos_num
 pos_num.rec|?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → (Π (n : pos_num), ?C n)
 pos_num.one|pos_num
@@ -22,6 +23,7 @@ pos_num.size|pos_num → pos_num
 pos_num.bit0|pos_num → pos_num
 pos_num.is_inhabited|inhabited pos_num
 pos_num.inc|pos_num → pos_num
+pos_num.induction_on|Π (n : pos_num), ?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → ?C n
 pos_num.bit1|pos_num → pos_num
 pos_num.rec|?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → (Π (n : pos_num), ?C n)
 pos_num.one|pos_num
@@ -33,6 +35,7 @@ pos_num.size|pos_num → pos_num
 pos_num.bit0|pos_num → pos_num
 pos_num.is_inhabited|inhabited pos_num
 pos_num.inc|pos_num → pos_num
+pos_num.induction_on|Π (n : pos_num), ?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → ?C n
 pos_num.bit1|pos_num → pos_num
 pos_num.rec|?C pos_num.one → (Π (a : pos_num), ?C a → ?C (pos_num.bit1 a)) → (Π (a : pos_num), ?C a → ?C (pos_num.bit0 a)) → (Π (n : pos_num), ?C n)
 pos_num.one|pos_num
diff --git a/tests/lean/run/beginend2.lean b/tests/lean/run/beginend2.lean
index 2489cd30cc..87cda77bc3 100644
--- a/tests/lean/run/beginend2.lean
+++ b/tests/lean/run/beginend2.lean
@@ -1,12 +1,12 @@
 import hott.path tools.tactic
 
 open path tactic
-open path (induction_on)
+open path (rec_on)
 
 definition concat_whisker2 {A} {x y z : A} (p p' : x ≈ y) (q q' : y ≈ z) (a : p ≈ p') (b : q ≈ q') :
   (whiskerR a q) ⬝ (whiskerL p' b) ≈ (whiskerL p b) ⬝ (whiskerR a q') :=
 begin
-  apply (induction_on b),
-  apply (induction_on a),
+  apply (rec_on b),
+  apply (rec_on a),
   apply ((concat_1p _)⁻¹),
 end
diff --git a/tests/lean/run/get_tac1.lean b/tests/lean/run/get_tac1.lean
index 25f7e05730..66f0cdc59f 100644
--- a/tests/lean/run/get_tac1.lean
+++ b/tests/lean/run/get_tac1.lean
@@ -4,8 +4,8 @@ open path
 definition concat_pV_p {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) : (p ⬝ q⁻¹) ⬝ q ≈ p :=
 begin
   generalize p,
-  apply (path.induction_on q),
+  apply (path.rec_on q),
   intro p,
-  apply (path.induction_on p),
+  apply (path.rec_on p),
   apply idp
 end
diff --git a/tests/lean/run/lift.lean b/tests/lean/run/lift.lean
index edbdc90060..fb38cf4885 100644
--- a/tests/lean/run/lift.lean
+++ b/tests/lean/run/lift.lean
@@ -11,8 +11,6 @@ rec (λ a, a) a
 theorem down_up {A : Type} (a : A) : down (up a) = a :=
 rfl
 
-protected theorem induction_on {A : Type} {P : lift A → Prop} (a : lift A) (H : ∀ (a : A), P (up a)) : P a :=
-rec H a
 
 theorem up_down {A : Type} (a' : lift A) : up (down a') = a' :=
 induction_on a' (λ a, rfl)
diff --git a/tests/lean/run/nat_bug.lean b/tests/lean/run/nat_bug.lean
index 347424814d..15a66dfcb6 100644
--- a/tests/lean/run/nat_bug.lean
+++ b/tests/lean/run/nat_bug.lean
@@ -7,8 +7,6 @@ zero : nat,
 succ : nat → nat
 definition refl := @eq.refl
 namespace nat
-theorem induction_on {P : nat → Prop} (a : nat) (H1 : P zero) (H2 : ∀ (n : nat) (IH : P n), P (succ n)) : P a
-:= nat.rec H1 H2 a
 
 definition pred (n : nat) := nat.rec zero (fun m x, m) n
 theorem pred_zero : pred zero = zero := refl _
diff --git a/tests/lean/run/nat_bug5.lean b/tests/lean/run/nat_bug5.lean
index 42dee77e5f..9d22b020a4 100644
--- a/tests/lean/run/nat_bug5.lean
+++ b/tests/lean/run/nat_bug5.lean
@@ -17,7 +17,6 @@ axiom add_zero_right (n : nat) : n + zero = n
 axiom mul_succ_right (n m : nat) : n * succ m = n * m + n
 axiom add_assoc (n m k : nat) : (n + m) + k = n + (m + k)
 axiom add_right_comm (n m k : nat) : n + m + k = n + k + m
-axiom induction_on {P : nat → Prop} (a : nat) (H1 : P zero) (H2 : ∀ (n : nat) (IH : P n), P (succ n)) : P a
 set_option unifier.max_steps 50000
 theorem mul_add_distr_left (n m k : nat) : (n + m) * k = n * k + m * k
 := induction_on k
diff --git a/tests/lean/slow/nat_bug2.lean b/tests/lean/slow/nat_bug2.lean
index 90969cd396..ec841c33ad 100644
--- a/tests/lean/slow/nat_bug2.lean
+++ b/tests/lean/slow/nat_bug2.lean
@@ -36,9 +36,6 @@ theorem nat_rec_zero {P : ℕ → Type} (x : P 0) (f : ∀m, P m → P (succ m))
 
 theorem nat_rec_succ {P : ℕ → Type} (x : P 0) (f : ∀m, P m → P (succ m)) (n : ℕ) : nat.rec x f (succ n) = f n (nat.rec x f n)
 
-theorem induction_on {P : ℕ → Prop} (a : ℕ) (H1 : P 0) (H2 : ∀ (n : ℕ) (IH : P n), P (succ n)) : P a
-:= nat.rec H1 H2 a
-
 -------------------------------------------------- succ pred
 
 theorem succ_ne_zero (n : ℕ) : succ n ≠ 0
diff --git a/tests/lean/slow/nat_wo_hints.lean b/tests/lean/slow/nat_wo_hints.lean
index 6e32aa37c7..e4950d608e 100644
--- a/tests/lean/slow/nat_wo_hints.lean
+++ b/tests/lean/slow/nat_wo_hints.lean
@@ -31,11 +31,6 @@ theorem nat_rec_zero {P : ℕ → Type} (x : P 0) (f : ∀m, P m → P (succ m))
 
 theorem nat_rec_succ {P : ℕ → Type} (x : P 0) (f : ∀m, P m → P (succ m)) (n : ℕ) : nat.rec x f (succ n) = f n (nat.rec x f n)
 
-theorem induction_on {P : ℕ → Prop} (a : ℕ) (H1 : P 0) (H2 : ∀ (n : ℕ) (IH : P n), P (succ n)) : P a
-:= nat.rec H1 H2 a
-
--------------------------------------------------- succ pred
-
 theorem succ_ne_zero (n : ℕ) : succ n ≠ 0
 := assume H : succ n = 0,
      have H2 : true = false, from
diff --git a/tests/lean/slow/path_groupoids.lean b/tests/lean/slow/path_groupoids.lean
index b72cfc51c7..fe251f9a29 100644
--- a/tests/lean/slow/path_groupoids.lean
+++ b/tests/lean/slow/path_groupoids.lean
@@ -22,13 +22,6 @@ notation x `≈`:50 y `:>`:0 A:0 := @path A x y
 notation `idp`:max := idpath _     -- TODO: can we / should we use `1`?
 
 namespace path
-  definition induction_on {A : Type} {a b : A} (p : a ≈ b)
-    {C : Π (b : A) (p : a ≈ b), Type} (H : C a (idpath a)) : C b p :=
-  path.rec H p
-end path
-
-open path
-
 -- Concatenation and inverse
 -- -------------------------
 
@@ -52,62 +45,62 @@ definition concat_11 {A : Type} (x : A) : idpath x ⬝ idpath x ≈ idpath x :=
 
 -- The identity path is a right unit.
 definition concat_p1 {A : Type} {x y : A} (p : x ≈ y) : p ⬝ idp ≈ p :=
-induction_on p idp
+rec_on p idp
 
 -- The identity path is a right unit.
 definition concat_1p {A : Type} {x y : A} (p : x ≈ y) : idp ⬝ p ≈ p :=
-induction_on p idp
+rec_on p idp
 
 -- Concatenation is associative.
 definition concat_p_pp {A : Type} {x y z t : A} (p : x ≈ y) (q : y ≈ z) (r : z ≈ t) :
   p ⬝ (q ⬝ r) ≈ (p ⬝ q) ⬝ r :=
-induction_on r (induction_on q idp)
+rec_on r (rec_on q idp)
 
 definition concat_pp_p {A : Type} {x y z t : A} (p : x ≈ y) (q : y ≈ z) (r : z ≈ t) :
   (p ⬝ q) ⬝ r ≈ p ⬝ (q ⬝ r) :=
-induction_on r (induction_on q idp)
+rec_on r (rec_on q idp)
 
 -- The left inverse law.
 definition concat_pV {A : Type} {x y : A} (p : x ≈ y) : p ⬝ p^ ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 -- The right inverse law.
 definition concat_Vp {A : Type} {x y : A} (p : x ≈ y) : p^ ⬝ p ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 
 -- Several auxiliary theorems about canceling inverses across associativity. These are somewhat
 -- redundant, following from earlier theorems.
 
 definition concat_V_pp {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : p^ ⬝ (p ⬝ q) ≈ q :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_p_Vp {A : Type} {x y z : A} (p : x ≈ y) (q : x ≈ z) : p ⬝ (p^ ⬝ q) ≈ q :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_pp_V {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : (p ⬝ q) ⬝ q^ ≈ p :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition concat_pV_p {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) : (p ⬝ q^) ⬝ q ≈ p :=
-induction_on q (take p, induction_on p idp) p
+rec_on q (take p, rec_on p idp) p
 
 -- Inverse distributes over concatenation
 definition inv_pp {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) : (p ⬝ q)^ ≈ q^ ⬝ p^ :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition inv_Vp {A : Type} {x y z : A} (p : y ≈ x) (q : y ≈ z) : (p^ ⬝ q)^ ≈ q^ ⬝ p :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 -- universe metavariables
 definition inv_pV {A : Type} {x y z : A} (p : x ≈ y) (q : z ≈ y) : (p ⬝ q^)^ ≈ q ⬝ p^ :=
-induction_on p (λq, induction_on q idp) q
+rec_on p (λq, rec_on q idp) q
 
 definition inv_VV {A : Type} {x y z : A} (p : y ≈ x) (q : z ≈ y) : (p^ ⬝ q^)^ ≈ q ⬝ p :=
-induction_on p (induction_on q idp)
+rec_on p (rec_on q idp)
 
 -- Inverse is an involution.
 definition inv_V {A : Type} {x y : A} (p : x ≈ y) : p^^ ≈ p :=
-induction_on p idp
+rec_on p idp
 
 
 -- Theorems for moving things around in equations
@@ -116,7 +109,7 @@ induction_on p idp
 definition moveR_Mp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   p ≈ (r^ ⬝ q) → (r ⬝ p) ≈ q :=
 have gen : Πp q, p ≈ (r^ ⬝ q) → (r ⬝ p) ≈ q, from
-  induction_on r
+  rec_on r
     (take p q,
       assume h : p ≈ idp^ ⬝ q,
       show idp ⬝ p ≈ q, from concat_1p _ ⬝ h ⬝ concat_1p _),
@@ -124,63 +117,63 @@ gen p q
 
 definition moveR_pM {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   r ≈ q ⬝ p^ → r ⬝ p ≈ q :=
-induction_on p (take q r h, (concat_p1 _ ⬝ h ⬝ concat_p1 _)) q r
+rec_on p (take q r h, (concat_p1 _ ⬝ h ⬝ concat_p1 _)) q r
 
 definition moveR_Vp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : x ≈ y) :
   p ≈ r ⬝ q → r^ ⬝ p ≈ q :=
-induction_on r (take p q h, concat_1p _ ⬝ h ⬝ concat_1p _) p q
+rec_on r (take p q h, concat_1p _ ⬝ h ⬝ concat_1p _) p q
 
 definition moveR_pV {A : Type} {x y z : A} (p : z ≈ x) (q : y ≈ z) (r : y ≈ x) :
   r ≈ q ⬝ p → r ⬝ p^ ≈ q :=
-induction_on p (take q r h, concat_p1 _ ⬝ h ⬝ concat_p1 _) q r
+rec_on p (take q r h, concat_p1 _ ⬝ h ⬝ concat_p1 _) q r
 
 definition moveL_Mp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   r^ ⬝ q ≈ p → q ≈ r ⬝ p :=
-induction_on r (take p q h, (concat_1p _)^ ⬝ h ⬝ (concat_1p _)^) p q
+rec_on r (take p q h, (concat_1p _)^ ⬝ h ⬝ (concat_1p _)^) p q
 
 definition moveL_pM {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : y ≈ x) :
   q ⬝ p^ ≈ r → q ≈ r ⬝ p :=
-induction_on p (take q r h, (concat_p1 _)^ ⬝ h ⬝ (concat_p1 _)^) q r
+rec_on p (take q r h, (concat_p1 _)^ ⬝ h ⬝ (concat_p1 _)^) q r
 
 definition moveL_Vp {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) (r : x ≈ y) :
   r ⬝ q ≈ p → q ≈ r^ ⬝ p :=
-induction_on r (take p q h, (concat_1p _)^ ⬝ h ⬝ (concat_1p _)^) p q
+rec_on r (take p q h, (concat_1p _)^ ⬝ h ⬝ (concat_1p _)^) p q
 
 definition moveL_pV {A : Type} {x y z : A} (p : z ≈ x) (q : y ≈ z) (r : y ≈ x) :
   q ⬝ p ≈ r → q ≈ r ⬝ p^ :=
-induction_on p (take q r h, (concat_p1 _)^ ⬝ h ⬝ (concat_p1 _)^) q r
+rec_on p (take q r h, (concat_p1 _)^ ⬝ h ⬝ (concat_p1 _)^) q r
 
 definition moveL_1M {A : Type} {x y : A} (p q : x ≈ y) :
   p ⬝ q^ ≈ idp → p ≈ q :=
-induction_on q (take p h, (concat_p1 _)^ ⬝ h)  p
+rec_on q (take p h, (concat_p1 _)^ ⬝ h)  p
 
 definition moveL_M1 {A : Type} {x y : A} (p q : x ≈ y) :
   q^ ⬝ p ≈ idp → p ≈ q :=
-induction_on q (take p h, (concat_1p _)^ ⬝ h)  p
+rec_on q (take p h, (concat_1p _)^ ⬝ h)  p
 
 definition moveL_1V {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   p ⬝ q ≈ idp → p ≈ q^ :=
-induction_on q (take p h, (concat_p1 _)^ ⬝ h)  p
+rec_on q (take p h, (concat_p1 _)^ ⬝ h)  p
 
 definition moveL_V1 {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   q ⬝ p ≈ idp → p ≈ q^ :=
-induction_on q (take p h, (concat_1p _)^ ⬝ h)  p
+rec_on q (take p h, (concat_1p _)^ ⬝ h)  p
 
 definition moveR_M1 {A : Type} {x y : A} (p q : x ≈ y) :
   idp ≈ p^ ⬝ q → p ≈ q :=
-induction_on p (take q h, h ⬝ (concat_1p _)) q
+rec_on p (take q h, h ⬝ (concat_1p _)) q
 
 definition moveR_1M {A : Type} {x y : A} (p q : x ≈ y) :
   idp ≈ q ⬝ p^ → p ≈ q :=
-induction_on p (take q h, h ⬝ (concat_p1 _)) q
+rec_on p (take q h, h ⬝ (concat_p1 _)) q
 
 definition moveR_1V {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   idp ≈ q ⬝ p → p^ ≈ q :=
-induction_on p (take q h, h ⬝ (concat_p1 _)) q
+rec_on p (take q h, h ⬝ (concat_p1 _)) q
 
 definition moveR_V1 {A : Type} {x y : A} (p : x ≈ y) (q : y ≈ x) :
   idp ≈ p ⬝ q → p^ ≈ q :=
-induction_on p (take q h, h ⬝ (concat_1p _)) q
+rec_on p (take q h, h ⬝ (concat_1p _)) q
 
 
 -- Transport
@@ -188,7 +181,7 @@ induction_on p (take q h, h ⬝ (concat_1p _)) q
 
 -- keep transparent, so transport _ idp p is definitionally equal to p
 definition transport {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) : P y :=
-path.induction_on p u
+path.rec_on p u
 
 definition transport_1 {A : Type} (P : A → Type) {x : A} (u : P x) : transport _ idp u ≈ u :=
 idp
@@ -199,7 +192,7 @@ idp
 notation p `#`:65 x:64 := transport _ p x
 
 definition ap ⦃A B : Type⦄ (f : A → B) {x y:A} (p : x ≈ y) : f x ≈ f y :=
-path.induction_on p idp
+path.rec_on p idp
 
 -- TODO: is this better than an alias? Note use of curly brackets
 definition ap01 := ap
@@ -210,18 +203,18 @@ definition pointwise_paths {A : Type} {P : A → Type} (f g : Πx, P x) : Type :
 infix `∼`:50 := pointwise_paths
 
 definition apD10 {A} {B : A → Type} {f g : Πx, B x} (H : f ≈ g) : f ∼ g :=
-λx, path.induction_on H idp
+λx, path.rec_on H idp
 
 definition ap10 {A B} {f g : A → B} (H : f ≈ g) : f ∼ g := apD10 H
 
 definition ap11 {A B} {f g : A → B} (H : f ≈ g) {x y : A} (p : x ≈ y) : f x ≈ g y :=
-induction_on H (induction_on p idp)
+rec_on H (rec_on p idp)
 
 -- TODO: Note that the next line breaks the proof!
--- opaque_hint (hiding induction_on)
+-- opaque_hint (hiding rec_on)
 -- set_option pp.implicit true
 definition apD {A:Type} {B : A → Type} (f : Πa:A, B a) {x y : A} (p : x ≈ y) : p # (f x) ≈ f y :=
-induction_on p idp
+rec_on p idp
 
 
 -- More theorems for moving things around in equations
@@ -229,19 +222,19 @@ induction_on p idp
 
 definition moveR_transport_p {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) (v : P y) :
   u ≈ p^ # v → p # u ≈ v :=
-induction_on p (take u v, id) u v
+rec_on p (take u v, id) u v
 
 definition moveR_transport_V {A : Type} (P : A → Type) {x y : A} (p : y ≈ x) (u : P x) (v : P y) :
   u ≈ p # v → p^ # u ≈ v :=
-induction_on p (take u v, id) u v
+rec_on p (take u v, id) u v
 
 definition moveL_transport_V {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (u : P x) (v : P y) :
   p # u ≈ v → u ≈ p^ # v :=
-induction_on p (take u v, id) u v
+rec_on p (take u v, id) u v
 
 definition moveL_transport_p {A : Type} (P : A → Type) {x y : A} (p : y ≈ x) (u : P x) (v : P y) :
   p^ # u ≈ v → u ≈ p # v :=
-induction_on p (take u v, id) u v
+rec_on p (take u v, id) u v
 
 
 -- Functoriality of functions
@@ -258,54 +251,54 @@ definition apD_1 {A B} (x : A) (f : forall x : A, B x) : apD f idp ≈ idp :> (f
 -- Functions commute with concatenation.
 definition ap_pp {A B : Type} (f : A → B) {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   ap f (p ⬝ q) ≈ (ap f p) ⬝ (ap f q) :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition ap_p_pp {A B : Type} (f : A → B) {w x y z : A} (r : f w ≈ f x) (p : x ≈ y) (q : y ≈ z) :
   r ⬝ (ap f (p ⬝ q)) ≈ (r ⬝ ap f p) ⬝ (ap f q) :=
-induction_on p (take r q, induction_on q (concat_p_pp r idp idp)) r q
+rec_on p (take r q, rec_on q (concat_p_pp r idp idp)) r q
 
 definition ap_pp_p {A B : Type} (f : A → B) {w x y z : A} (p : x ≈ y) (q : y ≈ z) (r : f z ≈ f w) :
   (ap f (p ⬝ q)) ⬝ r ≈ (ap f p) ⬝ (ap f q ⬝ r) :=
-induction_on p (take q, induction_on q (take r, concat_pp_p _ _ _)) q r
+rec_on p (take q, rec_on q (take r, concat_pp_p _ _ _)) q r
 
 -- Functions commute with path inverses.
 definition inverse_ap {A B : Type} (f : A → B) {x y : A} (p : x ≈ y) : (ap f p)^ ≈ ap f (p^) :=
-induction_on p idp
+rec_on p idp
 
 definition ap_V {A B : Type} (f : A → B) {x y : A} (p : x ≈ y) : ap f (p^) ≈ (ap f p)^ :=
-induction_on p idp
+rec_on p idp
 
 -- TODO: rename id to idmap?
 definition ap_idmap {A : Type} {x y : A} (p : x ≈ y) : ap id p ≈ p :=
-induction_on p idp
+rec_on p idp
 
 definition ap_compose {A B C : Type} (f : A → B) (g : B → C) {x y : A} (p : x ≈ y) :
   ap (g ∘ f) p ≈ ap g (ap f p) :=
-induction_on p idp
+rec_on p idp
 
 -- Sometimes we don't have the actual function [compose].
 definition ap_compose' {A B C : Type} (f : A → B) (g : B → C) {x y : A} (p : x ≈ y) :
   ap (λa, g (f a)) p ≈ ap g (ap f p) :=
-induction_on p idp
+rec_on p idp
 
 -- The action of constant maps.
 definition ap_const {A B : Type} {x y : A} (p : x ≈ y) (z : B) :
   ap (λu, z) p ≈ idp :=
-induction_on p idp
+rec_on p idp
 
 -- Naturality of [ap].
 definition concat_Ap {A B : Type} {f g : A → B} (p : forall x, f x ≈ g x) {x y : A} (q : x ≈ y) :
   (ap f q) ⬝ (p y) ≈ (p x) ⬝ (ap g q) :=
-induction_on q (concat_1p _ ⬝ (concat_p1 _)^)
+rec_on q (concat_1p _ ⬝ (concat_p1 _)^)
 
 -- Naturality of [ap] at identity.
 definition concat_A1p {A : Type} {f : A → A} (p : forall x, f x ≈ x) {x y : A} (q : x ≈ y) :
   (ap f q) ⬝ (p y) ≈ (p x) ⬝ q :=
-induction_on q (concat_1p _ ⬝ (concat_p1 _)^)
+rec_on q (concat_1p _ ⬝ (concat_p1 _)^)
 
 definition concat_pA1 {A : Type} {f : A → A} (p : forall x, x ≈ f x) {x y : A} (q : x ≈ y) :
   (p x) ⬝ (ap f q) ≈  q ⬝ (p y) :=
-induction_on q (concat_p1 _ ⬝ (concat_1p _)^)
+rec_on q (concat_p1 _ ⬝ (concat_1p _)^)
 
 --TODO: note that the Coq proof for the preceding is
 --
@@ -320,7 +313,7 @@ definition concat_pA_pp {A B : Type} {f g : A → B} (p : forall x, f x ≈ g x)
     {x y : A} (q : x ≈ y)
     {w z : B} (r : w ≈ f x) (s : g y ≈ z) :
   (r ⬝ ap f q) ⬝ (p y ⬝ s) ≈ (r ⬝ p x) ⬝ (ap g q ⬝ s) :=
-induction_on q (take s, induction_on s (take r, idp)) s r
+rec_on q (take s, rec_on s (take r, idp)) s r
 
 -- Action of [apD10] and [ap10] on paths
 -- -------------------------------------
@@ -331,11 +324,11 @@ definition apD10_1 {A} {B : A → Type} (f : Πx, B x) (x : A) : apD10 (idpath f
 
 definition apD10_pp {A} {B : A → Type} {f f' f'' : Πx, B x} (h : f ≈ f') (h' : f' ≈ f'') (x : A) :
   apD10 (h ⬝ h') x ≈ apD10 h x ⬝ apD10 h' x :=
-induction_on h (take h', induction_on h' idp) h'
+rec_on h (take h', rec_on h' idp) h'
 
 definition apD10_V {A : Type} {B : A → Type} {f g : Πx : A, B x} (h : f ≈ g) (x : A) :
   apD10 (h^) x ≈ (apD10 h x)^ :=
-induction_on h idp
+rec_on h idp
 
 definition ap10_1 {A B} {f : A → B} (x : A) : ap10 (idpath f) x ≈ idp := idp
 
@@ -347,7 +340,7 @@ definition ap10_V {A B} {f g : A→B} (h : f ≈ g) (x:A) : ap10 (h^) x ≈ (ap1
 -- [ap10] also behaves nicely on paths produced by [ap]
 definition ap_ap10 {A B C} (f g : A → B) (h : B → C) (p : f ≈ g) (a : A) :
   ap h (ap10 p a) ≈ ap10 (ap (λ f', h ∘ f') p) a:=
-induction_on p idp
+rec_on p idp
 
 
 -- Transport and the groupoid structure of paths
@@ -359,7 +352,7 @@ induction_on p idp
 
 definition transport_pp {A : Type} (P : A → Type) {x y z : A} (p : x ≈ y) (q : y ≈ z) (u : P x) :
   p ⬝ q # u ≈ q # p # u :=
-induction_on q (induction_on p idp)
+rec_on q (rec_on p idp)
 
 definition transport_pV {A : Type} (P : A → Type) {x y : A} (p : x ≈ y) (z : P y) :
   p # p^ # z ≈ z :=
@@ -379,27 +372,27 @@ theorem double_induction
     {C : Π(x y z : A), Π(p : x ≈ y), Π(q : y ≈ z), Type}
     (H : C x x x (idpath x) (idpath x)) :
   C x y z p q :=
-induction_on p (take z q, induction_on q H) z q
+rec_on p (take z q, rec_on q H) z q
 
 theorem double_induction2
     {A : Type} {x y z : A} (p : x ≈ y) (q : z ≈ y)
     {C : Π(x y z : A), Π(p : x ≈ y), Π(q : z ≈ y), Type}
     (H : C z z z (idpath z) (idpath z)) :
   C x y z p q :=
-induction_on p (take y q, induction_on q H) y q
+rec_on p (take y q, rec_on q H) y q
 
 theorem double_induction2'
   {A : Type} {x y z : A} (p : x ≈ y) (q : z ≈ y)
   {C : Π(x y z : A), Π(p : x ≈ y), Π(q : z ≈ y), Type}
   (H : C z z z (idpath z) (idpath z)) : C x y z p q :=
-induction_on p (take y q, induction_on q H) y q
+rec_on p (take y q, rec_on q H) y q
 
 theorem triple_induction
     {A : Type} {x y z w : A} (p : x ≈ y) (q : y ≈ z) (r : z ≈ w)
     {C : Π(x y z w : A), Π(p : x ≈ y), Π(q : y ≈ z), Π(r: z ≈ w), Type}
     (H : C x x x x (idpath x) (idpath x) (idpath x)) :
   C x y z w p q r :=
-induction_on p (take z q, induction_on q (take w r, induction_on r H)) z q w r
+rec_on p (take z q, rec_on q (take w r, rec_on r H)) z q w r
 
 -- try this again
 definition concat_pV_p_new {A : Type} {x y z : A} (p : x ≈ z) (q : y ≈ z) : (p ⬝ q^) ⬝ q ≈ p :=
@@ -416,13 +409,13 @@ triple_induction p q r (take u, idp) u
 --  Here is another coherence lemma for transport.
 definition transport_pVp {A} (P : A → Type) {x y : A} (p : x ≈ y) (z : P x) :
   transport_pV P p (transport P p z) ≈ ap (transport P p) (transport_Vp P p z)
-:= induction_on p idp
+:= rec_on p idp
 
 -- Dependent transport in a doubly dependent type.
 definition transportD {A : Type} (B : A → Type) (C : Π a : A, B a → Type)
     {x1 x2 : A} (p : x1 ≈ x2) (y : B x1) (z : C x1 y) :
   C x2 (p # y) :=
-induction_on p z
+rec_on p z
 
 -- Transporting along higher-dimensional paths
 definition transport2 {A : Type} (P : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q) (z : P x) :
@@ -432,28 +425,28 @@ definition transport2 {A : Type} (P : A → Type) {x y : A} {p q : x ≈ y} (r :
 definition transport2_is_ap10 {A : Type} (Q : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q)
     (z : Q x) :
   transport2 Q r z ≈ ap10 (ap (transport Q) r) z :=
-induction_on r idp
+rec_on r idp
 
 definition transport2_p2p {A : Type} (P : A → Type) {x y : A} {p1 p2 p3 : x ≈ y}
     (r1 : p1 ≈ p2) (r2 : p2 ≈ p3) (z : P x) :
   transport2 P (r1 ⬝ r2) z ≈ transport2 P r1 z ⬝ transport2 P r2 z :=
-induction_on r1 (induction_on r2 idp)
+rec_on r1 (rec_on r2 idp)
 
 -- TODO: another interesting case
 definition transport2_V {A : Type} (Q : A → Type) {x y : A} {p q : x ≈ y} (r : p ≈ q) (z : Q x) :
   transport2 Q (r^) z ≈ ((transport2 Q r z)^) :=
--- induction_on r idp -- doesn't work
-induction_on r (idpath (inverse (transport2 Q (idpath p) z)))
+-- rec_on r idp -- doesn't work
+rec_on r (idpath (inverse (transport2 Q (idpath p) z)))
 
 definition concat_AT {A : Type} (P : A → Type) {x y : A} {p q : x ≈ y} {z w : P x} (r : p ≈ q)
     (s : z ≈ w) :
   ap (transport P p) s  ⬝  transport2 P r w ≈ transport2 P r z  ⬝  ap (transport P q) s :=
-induction_on r (concat_p1 _ ⬝ (concat_1p _)^)
+rec_on r (concat_p1 _ ⬝ (concat_1p _)^)
 
 -- TODO (from Coq library): What should this be called?
 definition ap_transport {A} {P Q : A → Type} {x y : A} (p : x ≈ y) (f : Πx, P x → Q x) (z : P x) :
   f y (p # z) ≈ (p # (f x z)) :=
-induction_on p idp
+rec_on p idp
 
 
 -- Transporting in particular fibrations
@@ -471,34 +464,34 @@ subdirectory.  Here we consider only the most basic cases.
 -- Transporting in a constant fibration.
 definition transport_const {A B : Type} {x1 x2 : A} (p : x1 ≈ x2) (y : B) :
   transport (λx, B) p y ≈ y :=
-induction_on p idp
+rec_on p idp
 
 definition transport2_const {A B : Type} {x1 x2 : A} {p q : x1 ≈ x2} (r : p ≈ q) (y : B) :
   transport_const p y ≈ transport2 (λu, B) r y ⬝ transport_const q y :=
-induction_on r (concat_1p _)^
+rec_on r (concat_1p _)^
 
 -- Transporting in a pulled back fibration.
 definition transport_compose {A B} {x y : A} (P : B → Type) (f : A → B) (p : x ≈ y) (z : P (f x)) :
   transport (λx, P (f x)) p z  ≈  transport P (ap f p) z :=
-induction_on p idp
+rec_on p idp
 
 definition transport_precompose {A B C} (f : A → B) (g g' : B → C) (p : g ≈ g') :
   transport (λh : B → C, g ∘ f ≈ h ∘ f) p idp ≈ ap (λh, h ∘ f) p :=
-induction_on p idp
+rec_on p idp
 
 definition apD10_ap_precompose {A B C} (f : A → B) (g g' : B → C) (p : g ≈ g') (a : A) :
   apD10 (ap (λh : B → C, h ∘ f) p) a ≈ apD10 p (f a) :=
-induction_on p idp
+rec_on p idp
 
 definition apD10_ap_postcompose {A B C} (f : B → C) (g g' : A → B) (p : g ≈ g') (a : A) :
   apD10 (ap (λh : A → B, f ∘ h) p) a ≈ ap f (apD10 p a) :=
-induction_on p idp
+rec_on p idp
 
 -- TODO: another example where a term has to be given explicitly
 -- A special case of [transport_compose] which seems to come up a lot.
 definition transport_idmap_ap A (P : A → Type) x y (p : x ≈ y) (u : P x) :
   transport P p u ≈ transport (λz, z) (ap P p) u :=
-induction_on p (idpath (transport (λ (z : Type), z) (ap P (idpath x)) u))
+rec_on p (idpath (transport (λ (z : Type), z) (ap P (idpath x)) u))
 
 
 -- The behavior of [ap] and [apD]
@@ -507,7 +500,7 @@ induction_on p (idpath (transport (λ (z : Type), z) (ap P (idpath x)) u))
 -- In a constant fibration, [apD] reduces to [ap], modulo [transport_const].
 definition apD_const {A B} {x y : A} (f : A → B) (p: x ≈ y) :
   apD f p ≈ transport_const p (f x) ⬝ ap f p :=
-induction_on p idp
+rec_on p idp
 
 
 -- The 2-dimensional groupoid structure
@@ -516,13 +509,13 @@ induction_on p idp
 -- Horizontal composition of 2-dimensional paths.
 definition concat2 {A} {x y z : A} {p p' : x ≈ y} {q q' : y ≈ z} (h : p ≈ p') (h' : q ≈ q') :
   p ⬝ q ≈ p' ⬝ q' :=
-induction_on h (induction_on h' idp)
+rec_on h (rec_on h' idp)
 
 infixl `⬝⬝`:75 := concat2
 
 -- 2-dimensional path inversion
 definition inverse2 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) : p^ ≈ q^ :=
-induction_on h idp
+rec_on h idp
 
 -- Whiskering
 -- ----------
@@ -538,47 +531,47 @@ h ⬝⬝ idp
 -- -------------------------------
 
 definition cancelL {A} {x y z : A} (p : x ≈ y) (q r : y ≈ z) : (p ⬝ q ≈ p ⬝ r) → (q ≈ r) :=
-induction_on p (take r, induction_on r (take q a, (concat_1p q)^ ⬝ a)) r q
+rec_on p (take r, rec_on r (take q a, (concat_1p q)^ ⬝ a)) r q
 
 definition cancelR {A} {x y z : A} (p q : x ≈ y) (r : y ≈ z) : (p ⬝ r ≈ q ⬝ r) → (p ≈ q) :=
-induction_on r (take p, induction_on p (take q a, a ⬝ concat_p1 q)) p q
+rec_on r (take p, rec_on p (take q a, a ⬝ concat_p1 q)) p q
 
 -- Whiskering and identity paths.
 
 definition whiskerR_p1 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   (concat_p1 p)^ ⬝ whiskerR h idp ⬝ concat_p1 q ≈ h :=
-induction_on h (induction_on p idp)
+rec_on h (rec_on p idp)
 
 definition whiskerR_1p {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   whiskerR idp q ≈ idp :> (p ⬝ q ≈ p ⬝ q) :=
-induction_on q idp
+rec_on q idp
 
 definition whiskerL_p1 {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   whiskerL p idp ≈ idp :> (p ⬝ q ≈ p ⬝ q) :=
-induction_on q idp
+rec_on q idp
 
 definition whiskerL_1p {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   (concat_1p p) ^ ⬝ whiskerL idp h ⬝ concat_1p q ≈ h :=
-induction_on h (induction_on p idp)
+rec_on h (rec_on p idp)
 
 definition concat2_p1 {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   h ⬝⬝ idp ≈ whiskerR h idp :> (p ⬝ idp ≈ q ⬝ idp) :=
-induction_on h idp
+rec_on h idp
 
 definition concat2_1p {A : Type} {x y : A} {p q : x ≈ y} (h : p ≈ q) :
   idp ⬝⬝ h ≈ whiskerL idp h :> (idp ⬝ p ≈ idp ⬝ q) :=
-induction_on h idp
+rec_on h idp
 
 -- TODO: note, 4 inductions
 -- The interchange law for concatenation.
 definition concat_concat2 {A : Type} {x y z : A} {p p' p'' : x ≈ y} {q q' q'' : y ≈ z}
     (a : p ≈ p') (b : p' ≈ p'') (c : q ≈ q') (d : q' ≈ q'') :
   (a ⬝⬝ c) ⬝ (b ⬝⬝ d) ≈ (a ⬝ b) ⬝⬝ (c ⬝ d) :=
-induction_on d (induction_on c (induction_on b (induction_on a idp)))
+rec_on d (rec_on c (rec_on b (rec_on a idp)))
 
 definition concat_whisker {A} {x y z : A} (p p' : x ≈ y) (q q' : y ≈ z) (a : p ≈ p') (b : q ≈ q') :
   (whiskerR a q) ⬝ (whiskerL p' b) ≈ (whiskerL p b) ⬝ (whiskerR a q') :=
-induction_on b (induction_on a (concat_1p _)^)
+rec_on b (rec_on a (concat_1p _)^)
 
 -- Structure corresponding to the coherence equations of a bicategory.
 
@@ -588,12 +581,12 @@ definition pentagon {A : Type} {v w x y z : A} (p : v ≈ w) (q : w ≈ x) (r :
     ⬝ concat_p_pp p (q ⬝ r) s
     ⬝ whiskerR (concat_p_pp p q r) s
   ≈ concat_p_pp p q (r ⬝ s) ⬝ concat_p_pp (p ⬝ q) r s :=
-induction_on p (take q, induction_on q (take r, induction_on r (take s, induction_on s idp))) q r s
+rec_on p (take q, rec_on q (take r, rec_on r (take s, rec_on s idp))) q r s
 
 -- The 3-cell witnessing the left unit triangle.
 definition triangulator {A : Type} {x y z : A} (p : x ≈ y) (q : y ≈ z) :
   concat_p_pp p idp q ⬝ whiskerR (concat_p1 p) q ≈ whiskerL p (concat_1p q) :=
-induction_on p (take q, induction_on q idp) q
+rec_on p (take q, rec_on q idp) q
 
 definition eckmann_hilton {A : Type} {x:A} (p q : idp ≈ idp :> (x ≈ x)) : p ⬝ q ≈ q ⬝ p :=
   (whiskerR_p1 p ⬝⬝ whiskerL_1p q)^
@@ -607,19 +600,20 @@ definition eckmann_hilton {A : Type} {x:A} (p q : idp ≈ idp :> (x ≈ x)) : p
 
 -- The action of functions on 2-dimensional paths
 definition ap02 {A B : Type} (f:A → B) {x y : A} {p q : x ≈ y} (r : p ≈ q) : ap f p ≈ ap f q :=
-induction_on r idp
+rec_on r idp
 
 definition ap02_pp {A B} (f : A → B) {x y : A} {p p' p'' : x ≈ y} (r : p ≈ p') (r' : p' ≈ p'') :
   ap02 f (r ⬝ r') ≈ ap02 f r ⬝ ap02 f r' :=
-induction_on r (induction_on r' idp)
+rec_on r (rec_on r' idp)
 
 definition ap02_p2p {A B} (f : A→B) {x y z : A} {p p' : x ≈ y} {q q' :y ≈ z} (r : p ≈ p')
     (s : q ≈ q') :
   ap02 f (r ⬝⬝ s) ≈   ap_pp f p q
                       ⬝ (ap02 f r  ⬝⬝  ap02 f s)
                       ⬝ (ap_pp f p' q')^ :=
-induction_on r (induction_on s (induction_on q (induction_on p idp)))
+rec_on r (rec_on s (rec_on q (rec_on p idp)))
 
 definition apD02 {A : Type} {B : A → Type} {x y : A} {p q : x ≈ y} (f : Π x, B x) (r : p ≈ q) :
   apD f p ≈ transport2 B r (f x) ⬝ apD f q :=
-induction_on r (concat_1p _)^
+rec_on r (concat_1p _)^
+end path