lean2/library/init/sigma.lean
2015-02-11 14:09:25 -08:00

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/-
Copyright (c) 2014 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Module: init.sigma
Author: Leonardo de Moura, Jeremy Avigad, Floris van Doorn
-/
prelude
import init.datatypes init.num init.wf init.logic init.tactic
definition dpair := @sigma.mk
notation `Σ` binders `,` r:(scoped P, sigma P) := r
-- notation for n-ary tuples; input ⟨ ⟩ as \< \>
notation `⟨`:max t:(foldr `,` (e r, sigma.mk e r)) `⟩`:0 := t
namespace sigma
notation `pr₁` := pr1
notation `pr₂` := pr2
namespace ops
postfix `.1`:(max+1) := pr1
postfix `.2`:(max+1) := pr2
end ops
open ops well_founded
section
variables {A : Type} {B : A → Type}
variable (Ra : A → A → Prop)
variable (Rb : ∀ a, B a → B a → Prop)
-- Lexicographical order based on Ra and Rb
inductive lex : sigma B → sigma B → Prop :=
left : ∀{a₁ b₁} a₂ b₂, Ra a₁ a₂ → lex ⟨a₁, b₁⟩ ⟨a₂, b₂⟩,
right : ∀a {b₁ b₂}, Rb a b₁ b₂ → lex ⟨a, b₁⟩ ⟨a, b₂⟩
end
context
parameters {A : Type} {B : A → Type}
parameters {Ra : A → A → Prop} {Rb : Π a : A, B a → B a → Prop}
infix `≺`:50 := lex Ra Rb
definition lex.accessible {a} (aca : acc Ra a) (acb : ∀a, well_founded (Rb a)) : ∀ (b : B a), acc (lex Ra Rb) ⟨a, b⟩ :=
acc.rec_on aca
(λxa aca (iHa : ∀y, Ra y xa → ∀b : B y, acc (lex Ra Rb) ⟨y, b⟩),
λb : B xa, acc.rec_on (acb xa b)
(λxb acb
(iHb : ∀ (y : B xa), Rb xa y xb → acc (lex Ra Rb) ⟨xa, y⟩),
acc.intro ⟨xa, xb⟩ (λp (lt : p ≺ ⟨xa, xb⟩),
have aux : xa = xa → xb == xb → acc (lex Ra Rb) p, from
@sigma.lex.rec_on A B Ra Rb (λp₁ p₂, p₂.1 = xa → p₂.2 == xb → acc (lex Ra Rb) p₁)
p ⟨xa, xb⟩ lt
(λ (a₁ : A) (b₁ : B a₁) (a₂ : A) (b₂ : B a₂) (H : Ra a₁ a₂) (eq₂ : a₂ = xa) (eq₃ : b₂ == xb),
begin cases eq₂, exact (iHa a₁ H b₁) end)
(λ (a : A) (b₁ b₂ : B a) (H : Rb a b₁ b₂) (eq₂ : a = xa) (eq₃ : b₂ == xb),
begin cases eq₂, cases eq₃, exact (iHb b₁ H) end),
aux rfl !heq.refl)))
-- The lexicographical order of well founded relations is well-founded
definition lex.wf (Ha : well_founded Ra) (Hb : ∀ x, well_founded (Rb x)) : well_founded (lex Ra Rb) :=
well_founded.intro (λp, destruct p (λa b, lex.accessible (Ha a) Hb b))
end
end sigma