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.is_unit_or_eq> flags X1; Ltac.cut X2;
            [ intro; clear id
            | Ltac.cut X1; [ exact id | constructor 1; fail ] ]
Level 0: Backtrace:

p is used in conclusion.
Level 0: Backtrace:

p is used in conclusion.
Level 0: Backtrace:

p is used in conclusion.
Level 0: Backtrace:

p is used in conclusion.
Level 0: Backtrace:

p is used in conclusion.
Level 1: Backtrace:

p is used in conclusion.
Level 0: Backtrace:

p is used in conclusion.
Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 2: Backtrace:

Not convertible.
Level 1: Backtrace:

Not convertible.