Definition eqb_list {A: Type} (eqb_A: A -> A -> bool): list A -> list A -> bool :=
  fix eqb_list (l1 l2: list A): bool :=
    match l1, l2 with
    | nil, nil => true
    | a1 :: l1, a2 :: l2 => eqb_A a1 a2 && eqb_list l1 l2
    | _, _ => false
    end.

Lemma equiv_e2 : forall A B: Prop, A=B -> B -> A.