37 lines
1.3 KiB
Text
37 lines
1.3 KiB
Text
@include logic.pg
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section Category
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variable
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(Obj : *)
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(Hom : Obj -> Obj -> *)
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(id : forall (A : Obj), Hom A A)
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(comp : forall (A B C : Obj), Hom A B -> Hom B C -> Hom A C);
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hypothesis
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(id_l : forall (A B : Obj) (f : Hom A B), eq (Hom A B) (comp A A B (id A) f) f)
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(id_r : forall (A B : Obj) (f : Hom B A), eq (Hom A B) (comp B A A f (id A)) f)
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(assoc : forall (A B C D : Obj) (f : Hom A B) (g : Hom B C) (h : Hom C D),
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eq (Hom A D)
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(comp A B D f (comp B C D g h))
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(comp A C D (comp A B C f g) h));
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def initial (A : Obj) := forall (B : Obj), exists_uniq (Hom A B) (fun (f : Hom A B) => true);
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def terminal (A : Obj) := forall (B : Obj), exists_uniq (Hom B A) (fun (f : Hom B A) => true);
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section Inverses
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variable
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(A B : Obj)
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(f : Hom A B)
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(g : Hom B A);
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def inv_l := eq (Hom A A) (comp A B A f g) (id A);
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def inv_r := eq (Hom B B) (comp B A B g f) (id B);
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def inv := and inv_l inv_r;
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end Inverses
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def isomorphic (A B : Obj) :=
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exists (Hom A B) (fun (f : Hom A B) =>
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exists (Hom B A) (fun (g : Hom B A) =>
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inv A B f g));
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end Category
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