36 lines
1.2 KiB
Text
36 lines
1.2 KiB
Text
/-
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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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-/
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open decidable
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set_option structure.proj_mk_thm true
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structure subtype {A : Type} (P : A → Prop) :=
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tag :: (elt_of : A) (has_property : P elt_of)
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notation `{` binders `|` r:(scoped:1 P, subtype P) `}` := r
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namespace subtype
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variables {A : Type} {P : A → Prop}
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theorem tag_irrelevant {a : A} (H1 H2 : P a) : tag a H1 = tag a H2 :=
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rfl
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theorem tag_eq {a1 a2 : A} {H1 : P a1} {H2 : P a2} (H3 : a1 = a2) : tag a1 H1 = tag a2 H2 :=
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eq.subst H3 (take H2, tag_irrelevant H1 H2) H2
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protected theorem eq {a1 a2 : {x | P x}} : ∀(H : elt_of a1 = elt_of a2), a1 = a2 :=
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destruct a1 (take x1 H1, destruct a2 (take x2 H2 H, tag_eq H))
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protected definition is_inhabited [instance] {a : A} (H : P a) : inhabited {x | P x} :=
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inhabited.mk (tag a H)
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protected definition has_decidable_eq [instance] [H : decidable_eq A] : ∀ s₁ s₂ : {x | P x}, decidable (s₁ = s₂)
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| (tag v₁ p₁) (tag v₂ p₂) :=
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match H v₁ v₂ with
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| inl veq := begin left, substvars end
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| inr vne := begin right, intro h, injection h, contradiction end
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end
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end subtype
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