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
  ============================
   (let H := CoreTactics.block in
    noConfusionHom_All2_dep_obligation_1 A B R R' xs ys a a0 a0
      (noConfusionHom_All2_dep_obligation_2 A B R R' xs ys a a0 a0 eq_refl) =
    eq_refl)


DEBUG:Going to execute:
match goal with
           | |- ?T => change (let _ := CoreTactics.block in T)
           end