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feat(library/init/logic): add more congruence theorems

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Remark: the simplifier should be able to select the "right" one.
This commit is contained in:
Leonardo de Moura 2015-06-02 14:06:15 -07:00
parent 2f9005827c
commit 70d0dea02d
1 changed files with 46 additions and 8 deletions
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54
library/init/logic.lean
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@ -506,10 +506,10 @@ assume Hc, eq.rec_on (if_pos Hc) h
theorem implies_of_if_neg {c t e : Prop} [H : decidable c] (h : if c then t else e) : ¬c → e :=
assume Hnc, eq.rec_on (if_neg Hnc) h
theorem if_ctx_congr {A : Type} {b c : Prop} [dec_b : decidable b] {x y u v : A}
theorem if_ctx_congr {A : Type} {b c : Prop} [dec_b : decidable b] [dec_c : decidable c]
{x y u v : A}
(h_c : b ↔ c) (h_t : c → x = u) (h_e : ¬c → y = v) :
(if b then x else y) = (@ite c (decidable_of_decidable_of_iff dec_b h_c) A u v) :=
assert dec_c : decidable c, from decidable_of_decidable_of_iff dec_b h_c,
(if b then x else y) = (if c then u else v) :=
decidable.rec_on dec_b
(λ hp : b, calc
(if b then x else y)
@ -522,10 +522,41 @@ decidable.rec_on dec_b
... = v : h_e (iff.mp (not_iff_not_of_iff h_c) hn)
... = (if c then u else v) : if_neg (iff.mp (not_iff_not_of_iff h_c) hn))
theorem if_congr {A : Type} {b c : Prop} [dec_b : decidable b] {x y u v : A}
theorem if_congr {A : Type} {b c : Prop} [dec_b : decidable b] [dec_c : decidable c]
{x y u v : A}
(h_c : b ↔ c) (h_t : x = u) (h_e : y = v) :
(if b then x else y) = (if c then u else v) :=
@if_ctx_congr A b c dec_b dec_c x y u v h_c (λ h, h_t) (λ h, h_e)
theorem if_ctx_rw_congr {A : Type} {b c : Prop} [dec_b : decidable b] {x y u v : A}
(h_c : b ↔ c) (h_t : c → x = u) (h_e : ¬c → y = v) :
(if b then x else y) = (@ite c (decidable_of_decidable_of_iff dec_b h_c) A u v) :=
@if_ctx_congr A b c dec_b (decidable_of_decidable_of_iff dec_b h_c) x y u v h_c h_t h_e
theorem if_rw_congr {A : Type} {b c : Prop} [dec_b : decidable b] {x y u v : A}
(h_c : b ↔ c) (h_t : x = u) (h_e : y = v) :
(if b then x else y) = (@ite c (decidable_of_decidable_of_iff dec_b h_c) A u v) :=
@if_ctx_congr A b c dec_b x y u v h_c (λ h, h_t) (λ h, h_e)
@if_ctx_rw_congr A b c dec_b x y u v h_c (λ h, h_t) (λ h, h_e)
theorem if_congr_prop {b c x y u v : Prop} [dec_b : decidable b] [dec_c : decidable c]
(h_c : b ↔ c) (h_t : c → (x ↔ u)) (h_e : ¬c → (y ↔ v)) :
if b then x else y ↔ if c then u else v :=
decidable.rec_on dec_b
(λ hp : b, calc
(if b then x else y)
↔ x : iff.of_eq (if_pos hp)
... ↔ u : h_t (iff.mp h_c hp)
... ↔ (if c then u else v) : iff.of_eq (if_pos (iff.mp h_c hp)))
(λ hn : ¬b, calc
(if b then x else y)
↔ y : iff.of_eq (if_neg hn)
... ↔ v : h_e (iff.mp (not_iff_not_of_iff h_c) hn)
... ↔ (if c then u else v) : iff.of_eq (if_neg (iff.mp (not_iff_not_of_iff h_c) hn)))
theorem if_rw_congr_prop {b c x y u v : Prop} [dec_b : decidable b]
(h_c : b ↔ c) (h_t : c → (x ↔ u)) (h_e : ¬c → (y ↔ v)) :
if b then x else y ↔ (@ite c (decidable_of_decidable_of_iff dec_b h_c) Prop u v) :=
@if_congr_prop b c x y u v dec_b (decidable_of_decidable_of_iff dec_b h_c) h_c h_t h_e
-- We use "dependent" if-then-else to be able to communicate the if-then-else condition
-- to the branches
@ -544,13 +575,12 @@ decidable.rec
(λ Hnc : ¬c, eq.refl (@dite c (decidable.inr Hnc) A t e))
H
theorem dif_ctx_congr {A : Type} {b c : Prop} [dec_b : decidable b]
theorem dif_ctx_congr {A : Type} {b c : Prop} [dec_b : decidable b] [dec_c : decidable c]
{x : b → A} {u : c → A} {y : ¬b → A} {v : ¬c → A}
(h_c : b ↔ c)
(h_t : ∀ (h : c), x (iff.mp' h_c h) = u h)
(h_e : ∀ (h : ¬c), y (iff.mp' (not_iff_not_of_iff h_c) h) = v h) :
(@dite b dec_b A x y) = (@dite c (decidable_of_decidable_of_iff dec_b h_c) A u v) :=
assert dec_c : decidable c, from decidable_of_decidable_of_iff dec_b h_c,
(@dite b dec_b A x y) = (@dite c dec_c A u v) :=
decidable.rec_on dec_b
(λ hp : b, calc
(if h : b then x h else y h)
@ -567,6 +597,14 @@ decidable.rec_on dec_b
... = v (iff.mp h_nc hn) : h_e
... = (if h : c then u h else v h) : dif_neg (iff.mp h_nc hn))
theorem dif_ctx_rw_congr {A : Type} {b c : Prop} [dec_b : decidable b]
{x : b → A} {u : c → A} {y : ¬b → A} {v : ¬c → A}
(h_c : b ↔ c)
(h_t : ∀ (h : c), x (iff.mp' h_c h) = u h)
(h_e : ∀ (h : ¬c), y (iff.mp' (not_iff_not_of_iff h_c) h) = v h) :
(@dite b dec_b A x y) = (@dite c (decidable_of_decidable_of_iff dec_b h_c) A u v) :=
@dif_ctx_congr A b c dec_b (decidable_of_decidable_of_iff dec_b h_c) x u y v h_c h_t h_e
-- Remark: dite and ite are "definitionally equal" when we ignore the proofs.
theorem dite_ite_eq (c : Prop) [H : decidable c] {A : Type} (t : A) (e : A) : dite c (λh, t) (λh, e) = ite c t e :=
rfl