66 lines
1.9 KiB
Text
66 lines
1.9 KiB
Text
/-
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Copyright (c) 2015 Floris van Doorn. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Module: hit.coeq
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Authors: Floris van Doorn
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Declaration of the coequalizer
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-/
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import .type_quotient
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open type_quotient eq
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namespace coeq
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context
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universe u
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parameters {A B : Type.{u}} (f g : A → B)
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inductive coeq_rel : B → B → Type :=
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| Rmk : Π(x : A), coeq_rel (f x) (g x)
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open coeq_rel
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local abbreviation R := coeq_rel
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definition coeq : Type := type_quotient coeq_rel -- TODO: define this in root namespace
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definition coeq_i (x : B) : coeq :=
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class_of R x
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/- cp is the name Coq uses. I don't know what it abbreviates, but at least it's short :-) -/
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definition cp (x : A) : coeq_i (f x) = coeq_i (g x) :=
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eq_of_rel (Rmk f g x)
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protected definition rec {P : coeq → Type} (P_i : Π(x : B), P (coeq_i x))
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(Pcp : Π(x : A), cp x ▹ P_i (f x) = P_i (g x)) (y : coeq) : P y :=
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begin
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fapply (type_quotient.rec_on y),
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{ intro a, apply P_i},
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{ intros [a, a', H], cases H, apply Pcp}
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end
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protected definition rec_on [reducible] {P : coeq → Type} (y : coeq)
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(P_i : Π(x : B), P (coeq_i x)) (Pcp : Π(x : A), cp x ▹ P_i (f x) = P_i (g x)) : P y :=
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rec P_i Pcp y
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protected definition elim {P : Type} (P_i : B → P)
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(Pcp : Π(x : A), P_i (f x) = P_i (g x)) (y : coeq) : P :=
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rec P_i (λx, !tr_constant ⬝ Pcp x) y
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protected definition elim_on [reducible] {P : Type} (y : coeq) (P_i : B → P)
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(Pcp : Π(x : A), P_i (f x) = P_i (g x)) : P :=
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elim P_i Pcp y
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definition rec_cp {P : coeq → Type} (P_i : Π(x : B), P (coeq_i x))
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(Pcp : Π(x : A), cp x ▹ P_i (f x) = P_i (g x))
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(x : A) : apD (rec P_i Pcp) (cp x) = sorry ⬝ Pcp x ⬝ sorry :=
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sorry
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definition elim_cp {P : Type} (P_i : B → P) (Pcp : Π(x : A), P_i (f x) = P_i (g x))
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(x : A) : ap (elim P_i Pcp) (cp x) = sorry ⬝ Pcp x ⬝ sorry :=
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sorry
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end
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end coeq
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