Goal:
  
  A : Type
  B : Type
  R : nat → A → B → Type
  n : nat
  x : A
  y : B
  l : list A
  r : list B
  r0 : R n x y
  a : All2i R (S n) l r
  r2 : R n x y
  b : All2i R (S n) l r
  e : {| pr1 := r0; pr2 := a |} = {| pr1 := r2; pr2 := b |}
  ============================
   (noConfusionHom_All2i_obligation_2 A B R n (x :: l) 
      (y :: r) (All2i_cons r0 a) (All2i_cons r2 b)
      (noConfusionHom_All2i_obligation_1 A B R n (x :: l) 
         (y :: r) (All2i_cons r0 a) (All2i_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