proposition: Theorem DisjointInv1 : forall (a : A) (L1 L2 : list A), Disjoint L1 (a :: L2) -> Disjoint L1 L2.
proof: Proof. intros a L1 L2 H'; inversion H'; apply DisjointDef. intros a0 H'0; red in |- *; intros H'1. lapply (H a0); [ intros H'3; apply H'3 | idtac ]; auto. Qed.
imports: Coq(Arith) Coq(Lexicographic_Exponentiation)