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feat(library/standard/bool): add band_assoc and bor_assoc theorems

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Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
This commit is contained in:
Leonardo de Moura 2014-07-27 12:50:57 -07:00
parent 4b2e403023
commit 25f7929ea3
1 changed files with 19 additions and 3 deletions
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22
library/standard/bool.lean
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@ -56,11 +56,19 @@ theorem bor_b0_right (a : bool) : a || '0 = a
theorem bor_id (a : bool) : a || a = a
:= induction_on a (refl ('0 || '0)) (refl ('1 || '1))
theorem bor_swap (a b : bool) : a || b = b || a
theorem bor_comm (a b : bool) : a || b = b || a
:= induction_on a
(induction_on b (refl ('0 || '0)) (refl ('0 || '1)))
(induction_on b (refl ('1 || '0)) (refl ('1 || '1)))
theorem bor_assoc (a b c : bool) : (a || b) || c = a || (b || c)
:= induction_on a
(calc ('0 || b) || c = b || c : {bor_b0_left b}
... = '0 || (b || c) : bor_b0_left (b || c)⁻¹)
(calc ('1 || b) || c = '1 || c : {bor_b1_left b}
... = '1 : bor_b1_left c
... = '1 || (b || c) : bor_b1_left (b || c)⁻¹)
definition band (a b : bool)
:= bool_rec '0 (bool_rec '0 '1 b) a
@ -81,11 +89,19 @@ theorem band_b1_right (a : bool) : a && '1 = a
theorem band_id (a : bool) : a && a = a
:= induction_on a (refl ('0 && '0)) (refl ('1 && '1))
theorem band_swap (a b : bool) : a && b = b && a
theorem band_comm (a b : bool) : a && b = b && a
:= induction_on a
(induction_on b (refl ('0 && '0)) (refl ('0 && '1)))
(induction_on b (refl ('1 && '0)) (refl ('1 && '1)))
theorem band_assoc (a b c : bool) : (a && b) && c = a && (b && c)
:= induction_on a
(calc ('0 && b) && c = '0 && c : {band_b0_left b}
... = '0 : band_b0_left c
... = '0 && (b && c) : band_b0_left (b && c)⁻¹)
(calc ('1 && b) && c = b && c : {band_b1_left b}
... = '1 && (b && c) : band_b1_left (b && c)⁻¹)
theorem band_eq_b1_elim_left {a b : bool} (H : a && b = '1) : a = '1
:= or_elim (dichotomy a)
(assume H0 : a = '0,
@ -97,7 +113,7 @@ theorem band_eq_b1_elim_left {a b : bool} (H : a && b = '1) : a = '1
(assume H1 : a = '1, H1)
theorem band_eq_b1_elim_right {a b : bool} (H : a && b = '1) : b = '1
:= band_eq_b1_elim_left (trans (band_swap b a) H)
:= band_eq_b1_elim_left (trans (band_comm b a) H)
definition bnot (a : bool) := bool_rec '1 '0 a