X-Git-Url: http://git.megacz.com/?p=coq-categories.git;a=blobdiff_plain;f=src%2FIsomorphisms_ch1_5.v;h=422d4bbf75c4dfb0c8a138ad22f238a6f2f7d538;hp=fd9e19a6d5462cdaa1ae5087e3e875cad7e54f34;hb=57dfee583c84915cb6b3aadfa1dba692681499b3;hpb=ff3003c261295c60d367580b6700396102eb5a9c

diff --git a/src/Isomorphisms_ch1_5.v b/src/Isomorphisms_ch1_5.v
index fd9e19a..422d4bb 100644
--- a/src/Isomorphisms_ch1_5.v
+++ b/src/Isomorphisms_ch1_5.v
@@ -1,6 +1,5 @@
 Generalizable All Variables.
-Require Import Preamble.
-Require Import General.
+Require Import Notations.
 Require Import Categories_ch1_3.
 Require Import Functors_ch1_4.
 
@@ -45,7 +44,7 @@ Definition iso_id `{C:Category}(A:C) : Isomorphic A A.
   Defined.
 
 (* the composition of two isomorphisms is an isomorphism *)
-Definition id_comp `{C:Category}{a b c:C}(i1:Isomorphic a b)(i2:Isomorphic b c) : Isomorphic a c.
+Definition iso_comp `{C:Category}{a b c:C}(i1:Isomorphic a b)(i2:Isomorphic b c) : Isomorphic a c.
   intros; apply (@Build_Isomorphic _ _ C a c (#i1 >>> #i2) (#i2⁻¹ >>> #i1⁻¹));
     setoid_rewrite juggle3;
     [ setoid_rewrite (iso_comp1 i2) | setoid_rewrite (iso_comp2 i1) ];
@@ -53,6 +52,7 @@ Definition id_comp `{C:Category}{a b c:C}(i1:Isomorphic a b)(i2:Isomorphic b c)
     [ setoid_rewrite (iso_comp1 i1) | setoid_rewrite (iso_comp2 i2) ];
     reflexivity.
   Defined.
+Notation "a >>≅>> b" := (iso_comp a b).
 
 Definition functors_preserve_isos `{C1:Category}`{C2:Category}{Fo}(F:Functor C1 C2 Fo){a b:C1}(i:Isomorphic a b)
   : Isomorphic (F a) (F b).
@@ -102,3 +102,48 @@ Lemma iso_shift_left' `{C:Category} : forall {a b c:C}(f:a~>b)(g:a~>c)(i:Isomorp
   symmetry.
   apply right_identity.
   Qed.  
+
+Lemma isos_forward_equal_then_backward_equal `{C:Category}{a}{b}(i1 i2:a ≅ b) : #i1 ~~ #i2 ->  #i1⁻¹ ~~ #i2⁻¹.
+  intro H.
+  setoid_rewrite <- left_identity at 1.
+  setoid_rewrite <- (iso_comp2 i2).
+  setoid_rewrite associativity.
+  setoid_rewrite <- H.
+  setoid_rewrite iso_comp1.
+  setoid_rewrite right_identity.
+  reflexivity.
+  Qed.
+
+Lemma iso_inv_inv `{C:Category}{a}{b}(i:a ≅ b) : #(i⁻¹)⁻¹ ~~ #i.
+  unfold iso_inv; simpl.
+  reflexivity.
+  Qed.
+
+(* the next four lemmas are handy for setoid_rewrite; they let you avoid having to get the associativities right *)
+Lemma iso_comp2_right : forall `{C:Category}{a b}(i:a≅b) c (g:b~>c), iso_backward i >>> (iso_forward i >>> g) ~~ g.
+  intros.
+  setoid_rewrite <- associativity.
+  setoid_rewrite iso_comp2.
+  apply left_identity.
+  Qed.
+
+Lemma iso_comp2_left : forall `{C:Category}{a b}(i:a≅b) c (g:c~>b), (g >>> iso_backward i) >>> iso_forward i ~~ g.
+  intros.
+  setoid_rewrite associativity.
+  setoid_rewrite iso_comp2.
+  apply right_identity.
+  Qed.
+
+Lemma iso_comp1_right : forall `{C:Category}{a b}(i:a≅b) c (g:a~>c), iso_forward i >>> (iso_backward i >>> g) ~~ g.
+  intros.
+  setoid_rewrite <- associativity.
+  setoid_rewrite iso_comp1.
+  apply left_identity.
+  Qed.
+
+Lemma iso_comp1_left : forall `{C:Category}{a b}(i:a≅b) c (g:c~>a), (g >>> iso_forward i) >>> iso_backward i ~~ g.
+  intros.
+  setoid_rewrite associativity.
+  setoid_rewrite iso_comp1.
+  apply right_identity.
+  Qed.