Goal:
  
  A : Type
  P : A → Prop
  p : A → bool
  x : A
  l : list A
  H : P x
  H0 : Forall P l
  IHForall : ∀ p : A → bool, (∀ x : A, P x → p x) → forallb p l
  H1 : ∀ x : A, P x → p x
  ============================
   (is_true (p x))


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 := ∀ x : A, P x → p x
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.