...

diff --git a/helm/software/matita/nlibrary/algebra/magmas.ma b/helm/software/matita/nlibrary/algebra/magmas.ma
index df39c1b3042a50683ae7a817c7b7d96656a02866..22289b3c2c6e486d47c4e68d2fca99b4953aea41 100644 (file)
--- a/helm/software/matita/nlibrary/algebra/magmas.ma
+++ b/helm/software/matita/nlibrary/algebra/magmas.ma
@@ -66,11 +66,17 @@ nqed.
 ndefinition counter_image: ∀A,B. (A → B) → Ω \sup B → Ω \sup A ≝
  λA,B,f,Sb. {x | ∃y. y ∈ Sb ∧ f x = y}.
  
-(*
 ndefinition mm_counter_image:
  ∀A,B. ∀Ma: magma A. ∀Mb: magma B. magma_morphism ?? Ma Mb → magma A.
   #A; #B; #Ma; #Mb; #f;
   napply (mk_magma ???)
    [ napply (counter_image ?? f Mb)
-   | #x; #y; nwhd in ⊢ (% → % → ?); *; #y0; *; #Hy0; #H 
-*)
\ No newline at end of file
+   | #x; #y; nwhd in ⊢ (% → % → ?); *; #x0; *; #Hx0; #Hx1; *; #y0; *; #Hy0; #Hy1; nwhd;
+     napply (ex_intro ????)
+      [ napply (op ? x0 y0)
+      | napply (conj ????)
+         [ napply (op_closed ??????); nassumption
+         | nrewrite < Hx1;
+           nrewrite < Hy1;
+           napply (mmprop ?? f ??)]##]
+nqed.
\ No newline at end of file