Goal:
    A : Type  n : nat  hd : A  tl : list A  H : S n < #|hd :: tl|
  ============================
   (S n ≤ #|tl|)


DEBUG:Going to execute:
fun tac => match goal with
                      | H:?f ?a = ?f' ?a' |- _ => tac H
                      end