Goal:
  
  A : Type
  B : Type
  R : nat → A → B → Type
  n : nat
  l0 : list A
  l : list B
  a : All2i R n l0 l
  ============================
   (let H := CoreTactics.block in
    noConfusionHom_All2i_obligation_1 A B R n l0 l a a
      (noConfusionHom_All2i_obligation_2 A B R n l0 l a a eq_refl) = eq_refl)


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