63 lines
1.9 KiB
Text
63 lines
1.9 KiB
Text
-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
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-- Released under Apache 2.0 license as described in the file LICENSE.
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-- Author: Leonardo de Moura, Jeremy Avigad
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-- data.prod
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-- =========
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-- The cartesian product.
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import logic.classes.inhabited logic.core.eq logic.classes.decidable
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open inhabited decidable
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inductive prod (A B : Type) : Type :=
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pair : A → B → prod A B
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infixr `×` := prod
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-- notation for n-ary tuples
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notation `(` h `,` t:(foldl `,` (e r, pair r e) h) `)` := t
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namespace prod
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section
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parameters {A B : Type}
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abbreviation pr1 (p : prod A B) := prod_rec (λ x y, x) p
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abbreviation pr2 (p : prod A B) := prod_rec (λ x y, y) p
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theorem pr1_pair (a : A) (b : B) : pr1 (a, b) = a :=
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rfl
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theorem pr2_pair (a : A) (b : B) : pr2 (a, b) = b :=
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rfl
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-- TODO: remove prefix when we can protect it
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theorem pair_destruct {P : A × B → Prop} (p : A × B) (H : ∀a b, P (a, b)) : P p :=
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prod_rec H p
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theorem prod_ext (p : prod A B) : pair (pr1 p) (pr2 p) = p :=
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pair_destruct p (λx y, refl (x, y))
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theorem pair_eq {a1 a2 : A} {b1 b2 : B} (H1 : a1 = a2) (H2 : b1 = b2) : (a1, b1) = (a2, b2) :=
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subst H1 (subst H2 rfl)
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theorem prod_eq {p1 p2 : prod A B} : ∀ (H1 : pr1 p1 = pr1 p2) (H2 : pr2 p1 = pr2 p2), p1 = p2 :=
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pair_destruct p1 (take a1 b1, pair_destruct p2 (take a2 b2 H1 H2, pair_eq H1 H2))
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theorem prod_inhabited [instance] (H1 : inhabited A) (H2 : inhabited B) : inhabited (prod A B) :=
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inhabited_destruct H1 (λa, inhabited_destruct H2 (λb, inhabited_mk (pair a b)))
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theorem prod_eq_decidable [instance] (u v : A × B) (H1 : decidable (pr1 u = pr1 v))
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(H2 : decidable (pr2 u = pr2 v)) : decidable (u = v) :=
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have H3 : u = v ↔ (pr1 u = pr1 v) ∧ (pr2 u = pr2 v), from
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iff_intro
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(assume H, subst H (and_intro rfl rfl))
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(assume H, and_elim H (assume H4 H5, prod_eq H4 H5)),
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decidable_iff_equiv _ (iff_symm H3)
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end
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end prod
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