Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  x : A
  y : B
  l : list A
  l' : list B
  r : R x y
  rs : All2 R l l'
  r0 : R' x y r
  a0 : All2_dep R' rs
  r2 : R' x y r
  b : All2_dep R' rs
  e : {| pr1 := r0; pr2 := a0 |} = {| pr1 := r2; pr2 := b |}
  ============================
   (noConfusionHom_All2_dep_obligation_2 A B R R' 
      (x :: l) (y :: l') (All2_cons r rs) (All2_dep_cons r0 a0)
      (All2_dep_cons r2 b)
      (noConfusionHom_All2_dep_obligation_1 A B R R' 
         (x :: l) (y :: l') (All2_cons r rs) (All2_dep_cons r0 a0)
         (All2_dep_cons r2 b) e) = e)


DEBUG:Going to execute:
match type of H with
           | ?R ?x ?y =>
               let rhs := fresh in
               set (rhs := y) in *; pattern sigma rhs; clearbody rhs;
                destruct H; simpl
           end