lean2/library/data/prod.lean

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-- Copyright (c) 2014 Microsoft Corporation. All rights reserved.
-- Released under Apache 2.0 license as described in the file LICENSE.
-- Author: Leonardo de Moura, Jeremy Avigad
import logic.core.inhabited logic.core.eq logic.core.decidable
-- data.prod
-- =========
open inhabited decidable
-- The cartesian product.
inductive prod (A B : Type) : Type :=
mk : A → B → prod A B
definition pair := @prod.mk
infixr `×` := prod
-- notation for n-ary tuples
notation `(` h `,` t:(foldl `,` (e r, prod.mk r e) h) `)` := t
namespace prod
section
parameters {A B : Type}
definition pr1 (p : prod A B) := rec (λ x y, x) p
definition pr2 (p : prod A B) := rec (λ x y, y) p
theorem pr1_pair (a : A) (b : B) : pr1 (a, b) = a :=
rfl
theorem pr2_pair (a : A) (b : B) : pr2 (a, b) = b :=
rfl
protected theorem destruct {P : A × B → Prop} (p : A × B) (H : ∀a b, P (a, b)) : P p :=
rec H p
theorem prod_ext (p : prod A B) : pair (pr1 p) (pr2 p) = p :=
destruct p (λx y, eq.refl (x, y))
open eq.ops
theorem pair_eq {a1 a2 : A} {b1 b2 : B} (H1 : a1 = a2) (H2 : b1 = b2) : (a1, b1) = (a2, b2) :=
H1 ▸ H2 ▸ rfl
protected theorem equal {p1 p2 : prod A B} : ∀ (H1 : pr1 p1 = pr1 p2) (H2 : pr2 p1 = pr2 p2), p1 = p2 :=
destruct p1 (take a1 b1, destruct p2 (take a2 b2 H1 H2, pair_eq H1 H2))
protected definition is_inhabited [instance] (H1 : inhabited A) (H2 : inhabited B) : inhabited (prod A B) :=
inhabited.destruct H1 (λa, inhabited.destruct H2 (λb, inhabited.mk (pair a b)))
protected definition has_decidable_eq [instance] (H1 : decidable_eq A) (H2 : decidable_eq B) : decidable_eq (A × B) :=
take u v : A × B,
have H3 : u = v ↔ (pr1 u = pr1 v) ∧ (pr2 u = pr2 v), from
iff.intro
(assume H, H ▸ and.intro rfl rfl)
(assume H, and.elim H (assume H4 H5, equal H4 H5)),
decidable_iff_equiv _ (iff.symm H3)
end
end prod