Merge pull request #1648 from patrick-nicodemus/monoidal-cat

Author: Alizter

theories/Basics/Utf8.v

@@ -57,6 +57,7 @@ Reserved Notation "x ≠ y" (at level 70).
 Reserved Notation "x ⇸ y" (at level 99, right associativity, y at level 200).
 Reserved Notation "x ↠ y" (at level 99, right associativity, y at level 200).
 Reserved Notation "x ↪ y" (at level 99, right associativity, y at level 200).
+Reserved Notation "A ⊗ B" (at level 45, left associativity).
 (* Reserved Notation "∀  x .. y , P" (at level 200, x binder, y binder, right associativity). *)
 Reserved Notation "x ∨ y" (at level 85, right associativity).
 (* Reserved Notation "x ⊔ y" (at level 85, right associativity). *)

theories/Categories/Monoidal/MonoidalCategory.v

@@ -0,0 +1,111 @@
+Require Import Basics Basics.Utf8 Basics.Tactics.
+Require Import implementations.list.
+Require Import Category.Core Category.Prod Category.Morphisms.
+Require Import NatCategory.
+Require Import Functor.Core Functor.Identity Functor.Composition.Core Functor.Prod.Core
+        Functor.Utf8.
+Require Import NaturalTransformation.Core NaturalTransformation.Isomorphisms NaturalTransformation.Identity NaturalTransformation.Prod.
+Require Import NaturalTransformation.Composition.Core.
+Require Import FunctorCategory.Core FunctorCategory.Morphisms.
+Require Import ProductLaws.
+Require Import Cat.Core.
+
+Set Universe Polymorphism.
+Set Implicit Arguments.
+Generalizable All Variables.
+Set Asymmetric Patterns.
+
+Section MonoidalStructure.
+  Context `{Funext}.
+
+Local Notation "x --> y" := (morphism _ x y).
+
+Section MonoidalCategoryConcepts.
+  Variable C : PreCategory.
+  Variable tensor : ((C * C) -> C)%category.
+  Variable I : C.
+  
+  Local Notation "A ⊗ B" := (tensor (Datatypes.pair A B)).
+
+  Local Open Scope functor_scope.
+  Definition right_assoc := (tensor ∘ (Functor.Prod.pair 1 tensor) )%functor.
+  Definition left_assoc :=  tensor ∘
+                                   (Functor.Prod.pair tensor 1) ∘
+                                   (Associativity.functor _ _ _).
+
+  Definition associator := NaturalIsomorphism right_assoc left_assoc.
+  (* Orientation  (A ⊗ B) ⊗ C -> A ⊗ (B ⊗ C) *)
+  Definition pretensor (A : C) := Core.induced_snd tensor A.
+  Definition I_pretensor := pretensor I.
+  Definition posttensor (A : C) := Core.induced_fst tensor A.
+  Definition I_posttensor := posttensor I.
+  Definition left_unitor := NaturalIsomorphism I_pretensor 1.
+  Definition right_unitor := NaturalIsomorphism I_posttensor 1.
+
+  Close Scope functor_scope.
+  
+  Variable alpha : associator.
+  Variable lambda : left_unitor.
+  Variable rho : right_unitor.
+  Notation alpha_nat_trans := ((@morphism_isomorphic
+                                  (C * (C * C) -> C)%category right_assoc left_assoc) alpha).
+  Notation lambda_nat_trans := ((@morphism_isomorphic _ _ _) lambda).
+  Notation rho_nat_trans := ((@morphism_isomorphic _ _ _) rho).
+
+  Section coherence_laws.
+    Variable a b c d : C.
+  Local Definition P1 : (a ⊗ (b ⊗ (c ⊗ d))) --> (a ⊗ ((b ⊗ c) ⊗ d)).
+  Proof.
+    apply (morphism_of tensor); split; simpl.
+    - exact (Core.identity a).
+    - exact (alpha_nat_trans (b, (c, d))).
+  Defined.
+
+  Local Definition P2 : a ⊗ ((b ⊗ c) ⊗ d) --> (a ⊗ (b ⊗ c)) ⊗ d
+    := alpha_nat_trans (a, (b ⊗ c, d)).
+  Local Definition P3 : (a ⊗ (b ⊗ c)) ⊗ d --> ((a ⊗ b) ⊗ c ) ⊗ d.
+  Proof.
+    apply (morphism_of tensor); split; simpl.
+    - exact (alpha_nat_trans (a,_)).
+    - exact (Core.identity d).
+  Defined.
+  Local Definition P4 : a ⊗ (b ⊗ (c ⊗ d)) --> (a ⊗ b) ⊗ (c ⊗ d)
+    := alpha_nat_trans (a, (b, (c ⊗ d))).
+  Local Definition P5 : (a ⊗ b) ⊗ (c ⊗ d) --> ((a ⊗ b) ⊗ c ) ⊗ d
+    := alpha_nat_trans (a ⊗ b,(c, d)).
+
+  Local Open Scope morphism_scope.
+  Definition pentagon_eq := P3 o P2 o P1 = P5 o P4.
+  Close Scope morphism_scope.
+
+  Local Definition Q1 : (a ⊗ (I ⊗ b)) --> a ⊗ b.
+  Proof.
+    apply (morphism_of tensor); split; simpl.
+    - exact (Core.identity a).
+    - exact (lambda_nat_trans _).
+  Defined.
+
+  Local Definition Q2 : (a ⊗ (I ⊗ b)) --> a ⊗ b.
+  Proof.
+    refine (@Category.Core.compose _ _ ((a ⊗ I) ⊗ b) _ _ _).
+    - apply (morphism_of tensor); split; simpl.
+      + exact (rho_nat_trans a).
+      + exact (Core.identity b).
+    - exact (alpha_nat_trans (a,(I,b))).
+  Defined.
+  Definition triangle_eq := Q1 = Q2.
+  End coherence_laws.
+End MonoidalCategoryConcepts.
+
+Class MonoidalStructure (C : PreCategory) :=
+  Build_MonoidalStructure {
+    tensor : (C * C -> C)%category;
+    I : C;
+    alpha : associator tensor;
+    lambda : left_unitor tensor I;
+    rho : right_unitor tensor I;
+    pentagon_eq_holds : forall a b c d : C, pentagon_eq alpha a b c d;
+    triangle_eq_holds : forall a b : C, triangle_eq alpha lambda rho a b;
+  }.
+
+End MonoidalStructure.