Definition is_RInt (f : R -> V) (a b : R) (If : V) :=
  filterlim (fun ptd => scal (sign (b-a)) (Riemann_sum f ptd)) (Riemann_fine a b) (locally If).Definition ex_RInt (f : R -> V) (a b : R) :=
  exists If : V, is_RInt f a b If.

Lemma norm_RInt_le_const_abs : forall (f : R -> V) (a b : R) (lf : V) (M : R), (forall x, Rmin a b <= x <= Rmax a b -> norm (f x) <= M) -> is_RInt f a b lf -> norm lf <= Rabs (b - a) * M.