lean2/library/data/sigma.lean
2014-09-19 15:54:32 -07:00

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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
open inhabited eq_ops
inductive sigma {A : Type} (B : A → Type) : Type :=
dpair : Πx : A, B x → sigma B
notation `Σ` binders `,` r:(scoped P, sigma P) := r
namespace sigma
section
parameters {A : Type} {B : A → Type}
definition dpr1 (p : Σ x, B x) : A := rec (λ a b, a) p
definition dpr2 (p : Σ x, B x) : B (dpr1 p) := rec (λ a b, b) p
theorem dpr1_dpair (a : A) (b : B a) : dpr1 (dpair a b) = a := rfl
theorem dpr2_dpair (a : A) (b : B a) : dpr2 (dpair a b) = b := rfl
protected theorem destruct {P : sigma B → Prop} (p : sigma B) (H : ∀a b, P (dpair a b)) : P p :=
rec H p
theorem dpair_ext (p : sigma B) : dpair (dpr1 p) (dpr2 p) = p :=
destruct p (take a b, rfl)
theorem dpair_eq {a₁ a₂ : A} {b₁ : B a₁} {b₂ : B a₂} (H₁ : a₁ = a₂) (H₂ : eq.rec_on H₁ b₁ = b₂) :
dpair a₁ b₁ = dpair a₂ b₂ :=
eq.rec_on H₁
(λ (b₂ : B a₁) (H₁ : a₁ = a₁) (H₂ : eq.rec_on H₁ b₁ = b₂),
calc
dpair a₁ b₁ = dpair a₁ (eq.rec_on H₁ b₁) : {(eq.rec_on_id H₁ b₁)⁻¹}
... = dpair a₁ b₂ : {H₂})
b₂ H₁ H₂
protected theorem equal {p₁ p₂ : Σx : A, B x} :
∀(H₁ : dpr1 p₁ = dpr1 p₂) (H₂ : eq.rec_on H₁ (dpr2 p₁) = (dpr2 p₂)), p₁ = p₂ :=
destruct p₁ (take a₁ b₁, destruct p₂ (take a₂ b₂ H₁ H₂, dpair_eq H₁ H₂))
protected theorem is_inhabited [instance] (H₁ : inhabited A) (H₂ : inhabited (B (default A))) :
inhabited (sigma B) :=
inhabited.destruct H₁ (λa, inhabited.destruct H₂ (λb, inhabited.mk (dpair (default A) b)))
end
end sigma