induction l...
intros.
simpl.
apply Rplus_le_le_0_compat; intuition.
Qed.

Lemma RsumOver_constant_le (X: Set) (l: list X) (f: X -> R) (c: R):
(forall x, List.In x l -> f x <= c) -> RsumOver l f <= INR (length l) * c.