Goal:
  
  A : Type
  p : A → bool
  n : nat
  a : A
  l : list A
  IHl : ∀ n : nat, forallb p l → forallb p (skipn n l)
  H : is_true (p a && forallb p l)
  ============================
   (is_true (forallb p l))


DEBUG:Going to execute:
rewrite -> andb_and in H
Level 0: Backtrace:

Tactic failure: congruence failed.
Level 0: Backtrace:

Tactic failure: congruence failed.
DEBUG LTAC Evaluated term: IHl