Goal:
  
  A : Type
  p : A → bool
  q : A → bool
  l : list A
  H0 : ∀ x : A, In x l → p x ↔ q x
  ============================
   (∀ x : A, In x l → p x = q x)


DEBUG:Going to execute:
intros; eapply eq_true_iff_eq