Goal:
  
  A : Type
  p : A → bool
  n : nat
  a : A
  l : list A
  IHl : ∀ n : nat, forallb p l → forallb p (skipn n l)
  H0 : is_true (p a)
  H1 : is_true (forallb p l)
  ============================
   (is_true (forallb p l))


DEBUG:Going to execute:
<Coq.Init.Tauto.find_cut>
            ltac:(fun id0 id1 X2 =>
                    assert X2; [ exact (id0 id1) | clear id0 ])
Level 2: evaluation returns
<coq-core.plugins.tauto::is_disj@0>
where
tauto_flags := 
of type
tauto_flags
X1 := is_true (forallb p l)
of type
constr of type tacvalue

Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.