Goal:
  
  A : Type
  B : Type
  R : nat → A → B → Type
  n : nat
  b : All2i R n [] []
  e : NoConfusionHom_All2i A B R n [] [] All2i_nil b
  ============================
   (let H := CoreTactics.block in
    noConfusionHom_All2i_obligation_2 A B R n [] [] All2i_nil b
      (noConfusionHom_All2i_obligation_1 A B R n [] [] All2i_nil b e) = e)


DEBUG:Going to execute:
fun id =>
             CoreTactics.on_last_hyp
              ltac:(fun id' =>
                      match id' with
                      | id => idtac
                      | _ => revert id'; CoreTactics.revert_until id
                      end)