Goal:
  
  A : Type
  B : Type
  R : A → B → Type
  R' : ∀ (a : A) (b : B), R a b → Type
  xs : list A
  ys : list B
  a : All2 R xs ys
  a0 : All2_dep R' a
  b : All2_dep R' a
  e : NoConfusionHom_All2_dep A B R R' xs ys a a0 b
  ============================
   (noConfusionHom_All2_dep_obligation_2 A B R R' xs ys a a0 b
      (noConfusionHom_All2_dep_obligation_1 A B R R' xs ys a a0 b e) = e)


DEBUG:Going to execute:
match type of id with
           | sigma ?P =>
               let idx := fresh "idx" in
               destruct id as [idx id]; repeat CoreTactics.destruct_sigma idx;
                simpl in id
           | _ => idtac
           end