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.flatten_contravariant_disj> flags X1 X2 id
Level 2: evaluation returns
<coq-core.plugins.tauto::flatten_contravariant_conj@0>
where
tauto_flags := 
of type
tauto_flags
id := p
of type
constr
X2 := bool
of type
constr
X1 := A
of type
constr of type tacvalue

Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.