Fixpoint SubEquiN (N:nat) (x y:R) (del:posreal) : list R :=
match N with
| O => cons y nil
| S p => cons x (SubEquiN p (x + del) y del)
end.
Definition max_N (a b:R) (del:posreal) (h:a < b) : nat :=
let (N,_) := maxN del h in N.
Definition SubEqui (a b:R) (del:posreal) (h:a < b) : list R :=
SubEquiN (S (max_N del h)) a b del.

Lemma RiemannInt_P19 :
forall (f g:R -> R) (a b:R) (pr1:Riemann_integrable f a b)
(pr2:Riemann_integrable g a b),
a <= b ->
(forall x:R, a < x < b -> f x <= g x) -> RiemannInt pr1 <= RiemannInt pr2.