proposition: Lemma sigma_fnth_sup : forall n m, (m > n) -> sigma (fnth n) m == sigma (fnth n) (S n).
proof: Proof. intros. assert ((S n) <= m)%nat; auto with arith. elim H0; intros; auto. rewrite sigma_S; auto. setoid_rewrite H2. assert (m0 > n); auto with arith. setoid_rewrite (sigma_fnth_one n); auto. Qed.
imports: ALEA(Monads) ALEA(Utheory)