proposition: Lemma tail_cons_tail : forall (l1 l2: list A), l1 <> nil -> tail l1 ++ l2 = tail (l1 ++ l2).
proof: Proof. destruct l1. tauto. auto. Qed.
imports: CoLoR(LogicUtil EqUtil RelUtil BoolUtil NatUtil) Coq(Setoid SetoidList FunInd)