diff --git a/hott/init/nat.hlean b/hott/init/nat.hlean
index f60074408d..13c4977654 100644
--- a/hott/init/nat.hlean
+++ b/hott/init/nat.hlean
@@ -37,7 +37,7 @@ namespace nat
     nat.rec_on m
       (λ n, nat.cases_on n
         (inl rfl)
-        (λ m, inr (λ (e : succ m = zero), down (nat.no_confusion e))))
+        (λ m, inr (by contradiction)))
       (λ (m' : nat) (ih : ∀n, decidable (n = m')) (n : nat), nat.cases_on n
         (inr (λ h, down (nat.no_confusion h)))
         (λ (n' : nat),
@@ -79,8 +79,8 @@ namespace nat
   definition not_lt_zero (a : nat) : ¬ a < zero :=
   have aux : ∀ {b}, a < b → b = zero → empty, from
     λ b H, lt.cases_on H
-      (λ heq, down (nat.no_confusion heq))
-      (λ b h₁ heq, down (nat.no_confusion heq)),
+      (by contradiction)
+      (by contradiction),
   λ H, aux H rfl
 
   definition zero_lt_succ (a : nat) : zero < succ a :=
diff --git a/library/data/fintype.lean b/library/data/fintype.lean
index cb2aafe655..851d0acf2c 100644
--- a/library/data/fintype.lean
+++ b/library/data/fintype.lean
@@ -52,7 +52,7 @@ theorem find_discr_cons_of_eq {f g : A → B} {a : A} (l : list A) : f a = g a 
 assume eq, if_pos eq
 
 theorem ne_of_find_discr_eq_some {f g : A → B} {a : A} : ∀ {l}, find_discr f g l = some a → f a ≠ g a
-| []     e := option.no_confusion e
+| []     e := by contradiction
 | (x::l) e := by_cases
   (λ h : f x = g x,
      have aux : find_discr f g l = some a, by rewrite [find_discr_cons_of_eq l h at e]; exact e,
diff --git a/library/data/int/basic.lean b/library/data/int/basic.lean
index 02467860e0..6a49126162 100644
--- a/library/data/int/basic.lean
+++ b/library/data/int/basic.lean
@@ -108,10 +108,10 @@ int.cases_on a
     int.cases_on b
       (take n,
         if H : m = n then inl (congr_arg of_nat H) else inr (take H1, H (of_nat.inj H1)))
-      (take n', inr (assume H, int.no_confusion H)))
+      (take n', inr (by contradiction)))
   (take m',
     int.cases_on b
-      (take n, inr (assume H, int.no_confusion H))
+      (take n, inr (by contradiction))
       (take n',
         (if H : m' = n' then inl (congr_arg neg_succ_of_nat H) else
             inr (take H1, H (neg_succ_of_nat.inj H1)))))
diff --git a/library/data/list/basic.lean b/library/data/list/basic.lean
index c8a526c38f..7b1f4a017c 100644
--- a/library/data/list/basic.lean
+++ b/library/data/list/basic.lean
@@ -406,8 +406,8 @@ end nth
 open decidable
 definition has_decidable_eq {A : Type} [H : decidable_eq A] : ∀ l₁ l₂ : list A, decidable (l₁ = l₂)
 | []      []      := inl rfl
-| []      (b::l₂) := inr (λ H, list.no_confusion H)
-| (a::l₁) []      := inr (λ H, list.no_confusion H)
+| []      (b::l₂) := inr (by contradiction)
+| (a::l₁) []      := inr (by contradiction)
 | (a::l₁) (b::l₂) :=
   match H a b with
   | inl Hab  :=
diff --git a/library/data/list/perm.lean b/library/data/list/perm.lean
index 55697f28bc..6125ea73d2 100644
--- a/library/data/list/perm.lean
+++ b/library/data/list/perm.lean
@@ -24,17 +24,17 @@ theorem eq_nil_of_perm_nil {l₁ : list A} (p : [] ~ l₁) : l₁ = [] :=
 have gen : ∀ (l₂ : list A) (p : l₂ ~ l₁), l₂ = [] → l₁ = [], from
   take l₂ p, perm.induction_on p
     (λ h, h)
-    (λ x y l₁ l₂ p₁ r₁, list.no_confusion r₁)
-    (λ x y l e, list.no_confusion e)
+    (λ x y l₁ l₂ p₁ r₁, by contradiction)
+    (λ x y l e, by contradiction)
     (λ l₁ l₂ l₃ p₁ p₂ r₁ r₂ e, r₂ (r₁ e)),
 gen [] p rfl
 
 theorem not_perm_nil_cons (x : A) (l : list A) : ¬ [] ~ (x::l) :=
 have gen : ∀ (l₁ l₂ : list A) (p : l₁ ~ l₂), l₁ = [] → l₂ = (x::l) → false, from
   take l₁ l₂ p, perm.induction_on p
-    (λ e₁ e₂, list.no_confusion e₂)
-    (λ x l₁ l₂ p₁ r₁ e₁ e₂, list.no_confusion e₁)
-    (λ x y l e₁ e₂, list.no_confusion e₁)
+    (λ e₁ e₂, by contradiction)
+    (λ x l₁ l₂ p₁ r₁ e₁ e₂, by contradiction)
+    (λ x y l e₁ e₂, by contradiction)
     (λ l₁ l₂ l₃ p₁ p₂ r₁ r₂ e₁ e₂,
       begin
         rewrite [e₂ at *, e₁ at *],
diff --git a/library/data/nat/basic.lean b/library/data/nat/basic.lean
index 604f3a30f0..f470919786 100644
--- a/library/data/nat/basic.lean
+++ b/library/data/nat/basic.lean
@@ -47,7 +47,7 @@ nat.induction_on x
 /- successor and predecessor -/
 
 theorem succ_ne_zero (n : ℕ) : succ n ≠ 0 :=
-assume H, nat.no_confusion H
+by contradiction
 
 -- add_rewrite succ_ne_zero
 
diff --git a/library/data/num.lean b/library/data/num.lean
index 0f795e9e48..0662e05f72 100644
--- a/library/data/num.lean
+++ b/library/data/num.lean
@@ -61,17 +61,17 @@ namespace pos_num
 
   theorem decidable_eq [instance] : ∀ (a b : pos_num), decidable (a = b)
   | one      one      := inl rfl
-  | one      (bit0 b) := inr (λ H, pos_num.no_confusion H)
-  | one      (bit1 b) := inr (λ H, pos_num.no_confusion H)
-  | (bit0 a) one      := inr (λ H, pos_num.no_confusion H)
+  | one      (bit0 b) := inr (by contradiction)
+  | one      (bit1 b) := inr (by contradiction)
+  | (bit0 a) one      := inr (by contradiction)
   | (bit0 a) (bit0 b) :=
     match decidable_eq a b with
     | inl H₁  := inl (eq.rec_on H₁ rfl)
     | inr H₁  := inr (λ H, pos_num.no_confusion H (λ H₂, absurd H₂ H₁))
     end
-  | (bit0 a) (bit1 b) := inr (λ H, pos_num.no_confusion H)
-  | (bit1 a) one      := inr (λ H, pos_num.no_confusion H)
-  | (bit1 a) (bit0 b) := inr (λ H, pos_num.no_confusion H)
+  | (bit0 a) (bit1 b) := inr (by contradiction)
+  | (bit1 a) one      := inr (by contradiction)
+  | (bit1 a) (bit0 b) := inr (by contradiction)
   | (bit1 a) (bit1 b) :=
     match decidable_eq a b with
     | inl H₁  := inl (eq.rec_on H₁ rfl)
diff --git a/library/data/option.lean b/library/data/option.lean
index 49a6017801..6b87915dfc 100644
--- a/library/data/option.lean
+++ b/library/data/option.lean
@@ -20,7 +20,7 @@ namespace option
   not_false
 
   theorem none_ne_some {A : Type} (a : A) : none ≠ some a :=
-  assume H, option.no_confusion H
+  by contradiction
 
   theorem some.inj {A : Type} {a₁ a₂ : A} (H : some a₁ = some a₂) : a₁ = a₂ :=
   option.no_confusion H (λe, e)
diff --git a/library/data/sum.lean b/library/data/sum.lean
index 7a22cbdf76..db844dbf11 100644
--- a/library/data/sum.lean
+++ b/library/data/sum.lean
@@ -22,10 +22,10 @@ namespace sum
   variables {A B : Type}
 
   definition inl_ne_inr (a : A) (b : B) : inl a ≠ inr b :=
-  assume H, sum.no_confusion H
+  by contradiction
 
   definition inr_ne_inl (b : B) (a : A) : inr b ≠ inl a :=
-  assume H, sum.no_confusion H
+  by contradiction
 
   definition inl_inj {a₁ a₂ : A} : intro_left B a₁ = intro_left B a₂ → a₁ = a₂ :=
   assume H, sum.no_confusion H (λe, e)
@@ -45,8 +45,8 @@ namespace sum
       | decidable.inl hp := decidable.inl (hp ▸ rfl)
       | decidable.inr hn := decidable.inr (λ he, absurd (inl_inj he) hn)
     end
-  | has_decidable_eq (inl a₁) (inr b₂) := decidable.inr (λ e, sum.no_confusion e)
-  | has_decidable_eq (inr b₁) (inl a₂) := decidable.inr (λ e, sum.no_confusion e)
+  | has_decidable_eq (inl a₁) (inr b₂) := decidable.inr (by contradiction)
+  | has_decidable_eq (inr b₁) (inl a₂) := decidable.inr (by contradiction)
   | has_decidable_eq (inr b₁) (inr b₂) :=
     match h₂ b₁ b₂ with
       | decidable.inl hp := decidable.inl (hp ▸ rfl)
diff --git a/library/init/nat.lean b/library/init/nat.lean
index 5d25e5911e..cdfa8fa92f 100644
--- a/library/init/nat.lean
+++ b/library/init/nat.lean
@@ -44,8 +44,8 @@ namespace nat
     (acc.intro zero (λ (y : nat) (hlt : y < zero),
       have aux : ∀ {n₁}, y < n₁ → zero = n₁ → acc lt y, from
         λ n₁ hlt, nat.lt.cases_on hlt
-          (λ heq, nat.no_confusion heq)
-          (λ b hlt heq, nat.no_confusion heq),
+          (by contradiction)
+          (by contradiction),
       aux hlt rfl))
     (λ (n : nat) (ih : acc lt n),
       acc.intro (succ n) (λ (m : nat) (hlt : m < succ n),
@@ -68,8 +68,8 @@ namespace nat
   definition not_lt_zero (a : nat) : ¬ a < zero :=
   have aux : ∀ {b}, a < b → b = zero → false, from
     λ b H, lt.cases_on H
-      (λ heq, nat.no_confusion heq)
-      (λ b h₁ heq, nat.no_confusion heq),
+      (by contradiction)
+      (by contradiction),
   λ H, aux H rfl
 
   definition zero_lt_succ (a : nat) : zero < succ a :=
diff --git a/library/logic/examples/cont.lean b/library/logic/examples/cont.lean
index e8776600f1..b8f8401c1f 100644
--- a/library/logic/examples/cont.lean
+++ b/library/logic/examples/cont.lean
@@ -68,7 +68,7 @@ assert zero_eq_one : 0 = 1, from calc
   ... = β (α m)     : aux α (zω_eq_znkω m (M f + 1))
   ... = β (M f + 1) : by rewrite znkω_bound
   ... = 1           : by rewrite znkω_bound,
-nat.no_confusion zero_eq_one
+by contradiction
 end
 
 /-