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)
  ============================
   (p x && true = true)


DEBUG:Going to execute:
<coq-core.plugins.ltac::contradiction@0> $1
Level 0: Backtrace:

No primitive equality found.