Goal:
  
  A : Type
  P : A → Prop
  p : A → bool
  Hp : ∀ x : A, reflect (P x) (p x)
  x : A
  l : list A
  H : P x
  H0 : Forall P l
  IHForall : is_true (forallb p l)
  n : ¬ P x
  ============================
   (is_true false)


DEBUG:Going to execute:
(solve [ do_atom | use_hyps; do_ccl ]) ||
             fail "Cannot solve this goal"