End Grid.

(** Lemma 14.24 *)
(** Right distributivity of product over sum.*)
Lemma distr_r : forall O E E' A B C D AC BC DC,
Sum O E E' A B D -> Prod O E E' A C AC -> Prod O E E' B C BC ->
(Prod O E E' D C DC -> Sum O E E' AC BC DC).