Goal:
  
  A : Type
  P : A → Prop
  p : A → bool
  q : A → bool
  x : A
  l : list A
  H : P x
  H0 : Forall P l
  H1 : ∀ x : A, P x → p x = q x
  H2 : forallb p l = forallb q l
  ============================
   (p x && forallb p l = q x && forallb q l)


DEBUG:Going to execute:
f_equal