proposition: Theorem wp_o_head_c : forall l1 l2:list par, wp l1 -> wp l2 -> wp (open :: l1 ++ close :: l2).
proof: Proof. intros l1 l2 H1 H2. replace (open :: l1 ++ close :: l2) with ((open :: l1 ++ close :: nil) ++ l2). - apply wp_concat. apply wp_encapsulate; trivial. trivial. - repeat (simpl in |- *; rewrite <- app_assoc); simpl in |- *. trivial. Qed.
imports: List Arith