X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=src%2FIsomorphisms_ch1_5.v;h=65eaf4624265e65d2d567e8da5b31949cbce6bc7;hb=5f3bdb7947de02d8d60f1af77c999a3c80f7dbba;hp=fd9e19a6d5462cdaa1ae5087e3e875cad7e54f34;hpb=ff3003c261295c60d367580b6700396102eb5a9c;p=coq-categories.git

diff --git a/src/Isomorphisms_ch1_5.v b/src/Isomorphisms_ch1_5.v
index fd9e19a..65eaf46 100644
--- a/src/Isomorphisms_ch1_5.v
+++ b/src/Isomorphisms_ch1_5.v
@@ -45,7 +45,7 @@ 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) ];
@@ -102,3 +102,19 @@ 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.