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
  H : a0 = b
  ============================
   (NoConfusionHom_All2_dep A B R R' xs ys a a0 b)


DEBUG:Going to execute:
fun tac => lazymatch goal with
                      | H:_ |- _ => tac H
                      end