diff --git a/library/data/list/basic.lean b/library/data/list/basic.lean index 1fde8a5e92..a2e1b02eb8 100644 --- a/library/data/list/basic.lean +++ b/library/data/list/basic.lean @@ -33,166 +33,175 @@ section variable {T : Type} theorem induction_on [protected] {P : list T → Prop} (l : list T) (Hnil : P nil) - (Hind : forall x : T, forall l : list T, forall H : P l, P (cons x l)) : P l := + (Hind : ∀ (x : T) (l : list T), P l → P (x :: l)) : P l := rec Hnil Hind l theorem cases_on [protected] {P : list T → Prop} (l : list T) (Hnil : P nil) - (Hcons : forall x : T, forall l : list T, P (cons x l)) : P l := + (Hcons : ∀ (x : T) (l : list T), P (x :: l)) : P l := induction_on l Hnil (take x l IH, Hcons x l) abbreviation rec_on [protected] {A : Type} {C : list A → Type} (l : list A) - (H1 : C nil) (H2 : ∀ (h : A) (t : list A), C t → C (cons h t)) : C l := + (H1 : C nil) (H2 : Π (h : A) (t : list A), C t → C (h :: t)) : C l := rec H1 H2 l -notation `[` l:(foldr `,` (h t, cons h t) nil) `]` := l +notation `[` l:(foldr `,` (h t, h :: t) nil) `]` := l -- Concat -- ------ -definition concat (s t : list T) : list T := -rec t (fun x : T, fun l : list T, fun u : list T, cons x u) s +definition append (s t : list T) : list T := +rec t (λx l u, x :: u) s -infixl `++` : 65 := concat +infixl `++` : 65 := append -theorem nil_concat {t : list T} : nil ++ t = t +theorem nil_append {t : list T} : nil ++ t = t -theorem cons_concat {x : T} {s t : list T} : (x :: s) ++ t = x :: (s ++ t) +theorem cons_append {x : T} {s t : list T} : (x :: s) ++ t = x :: (s ++ t) -theorem concat_nil {t : list T} : t ++ nil = t := +theorem append_nil {t : list T} : t ++ nil = t := induction_on t rfl - (take (x : T) (l : list T) (H : concat l nil = l), - show concat (cons x l) nil = cons x l, from H ▸ rfl) + (take (x : T) (l : list T) (H : append l nil = l), + H ▸ rfl) -theorem concat_assoc {s t u : list T} : s ++ t ++ u = s ++ (t ++ u) := -induction_on s rfl - (take x l, - assume H : concat (concat l t) u = concat l (concat t u), +theorem append_assoc {s t u : list T} : s ++ t ++ u = s ++ (t ++ u) := +induction_on s + rfl + (take x l, assume H : (l ++ t) ++ u = l ++ (t ++ u), calc - concat (concat (cons x l) t) u = cons x (concat (concat l t) u) : rfl - ... = cons x (concat l (concat t u)) : {H} - ... = concat (cons x l) (concat t u) : rfl) + (x :: l) ++ t ++ u = x :: (l ++ t ++ u) : rfl + ... = x :: (l ++ (t ++ u)) : {H} + ... = (x :: l) ++ (t ++ u) : rfl) -- Length -- ------ -definition length : list T → ℕ := rec 0 (fun x l m, succ m) +definition length : list T → ℕ := +rec 0 (λx l m, succ m) -theorem length_nil : length (@nil T) = 0 := rfl +theorem length_nil : length (@nil T) = 0 theorem length_cons {x : T} {t : list T} : length (x :: t) = succ (length t) -theorem length_concat {s t : list T} : length (s ++ t) = length s + length t := +theorem length_append {s t : list T} : length (s ++ t) = length s + length t := induction_on s (calc - length (concat nil t) = length t : rfl - ... = zero + length t : {add_zero_left⁻¹} - ... = length (@nil T) + length t : rfl) + length (nil ++ t) = length t : rfl + ... = 0 + length t : {add_zero_left⁻¹} + ... = length nil + length t : rfl) (take x s, - assume H : length (concat s t) = length s + length t, + assume H : length (s ++ t) = length s + length t, calc - length (concat (cons x s) t ) = succ (length (concat s t)) : rfl - ... = succ (length s + length t) : {H} - ... = succ (length s) + length t : {add_succ_left⁻¹} - ... = length (cons x s) + length t : rfl) + length ((x :: s) ++ t ) = succ (length (s ++ t)) : rfl + ... = succ (length s + length t) : {H} + ... = succ (length s) + length t : {add_succ_left⁻¹} + ... = length (x :: s) + length t : rfl) -- add_rewrite length_nil length_cons -- Append -- ------ -definition append (x : T) : list T → list T := rec [x] (fun y l l', y :: l') +definition concat (x : T) : list T → list T := +rec [x] (λy l l', y :: l') -theorem append_nil {x : T} : append x nil = [x] +theorem concat_nil {x : T} : concat x nil = [x] -theorem append_cons {x y : T} {l : list T} : append x (y :: l) = y :: (append x l) +theorem concat_cons {x y : T} {l : list T} : concat x (y :: l) = y :: (concat x l) -theorem append_eq_concat {x : T} {l : list T} : append x l = l ++ [x] +theorem concat_eq_append {x : T} {l : list T} : concat x l = l ++ [x] -- add_rewrite append_nil append_cons -- Reverse -- ------- -definition reverse : list T → list T := rec nil (fun x l r, r ++ [x]) +definition reverse : list T → list T := +rec nil (λx l r, r ++ [x]) theorem reverse_nil : reverse (@nil T) = nil -theorem reverse_cons {x : T} {l : list T} : reverse (x :: l) = append x (reverse l) +theorem reverse_cons {x : T} {l : list T} : reverse (x :: l) = concat x (reverse l) theorem reverse_singleton {x : T} : reverse [x] = [x] -theorem reverse_concat {s t : list T} : reverse (s ++ t) = (reverse t) ++ (reverse s) := -induction_on s (concat_nil⁻¹) - (take x s, - assume IH : reverse (s ++ t) = concat (reverse t) (reverse s), +theorem reverse_append {s t : list T} : reverse (s ++ t) = (reverse t) ++ (reverse s) := +induction_on s + (append_nil⁻¹) + (take x s, assume IH : reverse (s ++ t) = (reverse t) ++ (reverse s), calc reverse ((x :: s) ++ t) = reverse (s ++ t) ++ [x] : rfl ... = reverse t ++ reverse s ++ [x] : {IH} - ... = reverse t ++ (reverse s ++ [x]) : concat_assoc + ... = reverse t ++ (reverse s ++ [x]) : append_assoc ... = reverse t ++ (reverse (x :: s)) : rfl) theorem reverse_reverse {l : list T} : reverse (reverse l) = l := -induction_on l rfl +induction_on l + rfl (take x l', assume H: reverse (reverse l') = l', show reverse (reverse (x :: l')) = x :: l', from calc reverse (reverse (x :: l')) = reverse (reverse l' ++ [x]) : rfl - ... = reverse [x] ++ reverse (reverse l') : reverse_concat + ... = reverse [x] ++ reverse (reverse l') : reverse_append ... = [x] ++ l' : {H} ... = x :: l' : rfl) -theorem append_eq_reverse_cons {x : T} {l : list T} : append x l = reverse (x :: reverse l) := -induction_on l rfl +theorem concat_eq_reverse_cons {x : T} {l : list T} : concat x l = reverse (x :: reverse l) := +induction_on l + rfl (take y l', - assume H : append x l' = reverse (x :: reverse l'), + assume H : concat x l' = reverse (x :: reverse l'), calc - append x (y :: l') = (y :: l') ++ [ x ] : append_eq_concat - ... = concat (reverse (reverse (y :: l'))) [ x ] : {reverse_reverse⁻¹} - ... = reverse (x :: (reverse (y :: l'))) : rfl) + concat x (y :: l') = (y :: l') ++ [x] : concat_eq_append + ... = reverse (reverse (y :: l')) ++ [x] : {reverse_reverse⁻¹} + ... = reverse (x :: (reverse (y :: l'))) : rfl) -- Head and tail -- ------------- -definition head (x : T) : list T → T := rec x (fun x l h, x) +definition head (x : T) : list T → T := +rec x (λx l h, x) -theorem head_nil {x : T} : head x (@nil T) = x +theorem head_nil {x : T} : head x nil = x theorem head_cons {x x' : T} {t : list T} : head x' (x :: t) = x theorem head_concat {s t : list T} {x : T} : s ≠ nil → (head x (s ++ t) = head x s) := cases_on s (take H : nil ≠ nil, absurd rfl H) - (take x s, take H : cons x s ≠ nil, + (take x s, take H : x :: s ≠ nil, calc - head x (concat (cons x s) t) = head x (cons x (concat s t)) : {cons_concat} - ... = x : {head_cons} - ... = head x (cons x s) : {head_cons⁻¹}) + head x ((x :: s) ++ t) = head x (x :: (s ++ t)) : {cons_append} + ... = x : {head_cons} + ... = head x (x :: s) : {head_cons⁻¹}) -definition tail : list T → list T := rec nil (fun x l b, l) +definition tail : list T → list T := +rec nil (λx l b, l) theorem tail_nil : tail (@nil T) = nil -theorem tail_cons {x : T} {l : list T} : tail (cons x l) = l +theorem tail_cons {x : T} {l : list T} : tail (x :: l) = l theorem cons_head_tail {x : T} {l : list T} : l ≠ nil → (head x l) :: (tail l) = l := cases_on l (assume H : nil ≠ nil, absurd rfl H) - (take x l, assume H : cons x l ≠ nil, rfl) + (take x l, assume H : x :: l ≠ nil, rfl) -- List membership -- --------------- -definition mem (x : T) : list T → Prop := rec false (fun y l H, x = y ∨ H) +definition mem (x : T) : list T → Prop := +rec false (λy l H, x = y ∨ H) infix `∈` := mem --- TODO: constructively, equality is stronger. Use that? -theorem mem_nil {x : T} : x ∈ nil ↔ false := iff.rfl +theorem mem_nil {x : T} : x ∈ nil ↔ false := +iff.rfl -theorem mem_cons {x y : T} {l : list T} : mem x (cons y l) ↔ (x = y ∨ mem x l) := iff.rfl +theorem mem_cons {x y : T} {l : list T} : mem x (y :: l) ↔ (x = y ∨ mem x l) := +iff.rfl theorem mem_concat_imp_or {x : T} {s t : list T} : x ∈ s ++ t → x ∈ s ∨ x ∈ t := induction_on s or.inr @@ -216,8 +225,8 @@ induction_on s (take H2 : x ∈ s, or.inr (IH (or.inl H2)))) (assume H1 : x ∈ t, or.inr (IH (or.inr H1)))) -theorem mem_concat {x : T} {s t : list T} : x ∈ s ++ t ↔ x ∈ s ∨ x ∈ t -:= iff.intro mem_concat_imp_or mem_or_imp_concat +theorem mem_concat {x : T} {s t : list T} : x ∈ s ++ t ↔ x ∈ s ∨ x ∈ t := +iff.intro mem_concat_imp_or mem_or_imp_concat theorem mem_split {x : T} {l : list T} : x ∈ l → ∃s t : list T, l = s ++ (x :: t) := induction_on l @@ -227,8 +236,7 @@ induction_on l assume H : x ∈ y :: l, or.elim H (assume H1 : x = y, - exists_intro nil - (exists_intro l (H1 ▸ rfl))) + exists_intro nil (exists_intro l (H1 ▸ rfl))) (assume H1 : x ∈ l, obtain s (H2 : ∃t : list T, l = s ++ (x :: t)), from IH H1, obtain t (H3 : l = s ++ (x :: t)), from H2, @@ -238,9 +246,9 @@ induction_on l theorem mem_is_decidable [instance] {H : decidable_eq T} {x : T} {l : list T} : decidable (mem x l) := rec_on l - (decidable.inr (iff.false_elim (@mem_nil x))) + (decidable.inr (iff.false_elim mem_nil)) (λ (h : T) (l : list T) (iH : decidable (mem x l)), - show decidable (mem x (cons h l)), from + show decidable (mem x (h :: l)), from decidable.rec_on iH (assume Hp : mem x l, decidable.rec_on (H x h) @@ -257,7 +265,7 @@ rec_on l assume H2 : x = h ∨ mem x l, or.elim H2 (assume Heq, absurd Heq Hne) (assume Hp, absurd Hp Hn), - have H2 : ¬mem x (cons h l), from + have H2 : ¬mem x (h :: l), from iff.elim_right (iff.flip_sign mem_cons) H1, decidable.inr H2))) @@ -265,12 +273,12 @@ rec_on l -- ---- definition find {H : decidable_eq T} (x : T) : list T → nat := -rec 0 (fun y l b, if x = y then 0 else succ b) +rec 0 (λy l b, if x = y then 0 else succ b) theorem find_nil {H : decidable_eq T} {f : T} : find f nil = 0 theorem find_cons {H : decidable_eq T} {x y : T} {l : list T} : - find x (cons y l) = if x = y then 0 else succ (find x l) + find x (y :: l) = if x = y then 0 else succ (find x l) theorem not_mem_find {H : decidable_eq T} {l : list T} {x : T} : ¬mem x l → find x l = length l := @@ -278,14 +286,14 @@ rec_on l (assume P₁ : ¬mem x nil, rfl) (take y l, assume iH : ¬mem x l → find x l = length l, - assume P₁ : ¬mem x (cons y l), + assume P₁ : ¬mem x (y :: l), have P₂ : ¬(x = y ∨ mem x l), from iff.elim_right (iff.flip_sign mem_cons) P₁, have P₃ : ¬x = y ∧ ¬mem x l, from (iff.elim_left not_or P₂), calc - find x (cons y l) = if x = y then 0 else succ (find x l) : find_cons - ... = succ (find x l) : if_neg (and.elim_left P₃) - ... = succ (length l) : {iH (and.elim_right P₃)} - ... = length (cons y l) : length_cons⁻¹) + find x (y :: l) = if x = y then 0 else succ (find x l) : find_cons + ... = succ (find x l) : if_neg (and.elim_left P₃) + ... = succ (length l) : {iH (and.elim_right P₃)} + ... = length (y :: l) : length_cons⁻¹) -- nth element -- -----------