(* Proof                                                                   *)
intros; tauto.
Qed.
(* End of proof                                                            *)

Lemma lem_or_and_conv_r :
forall a b c d : Prop,
(a \/ c) /\ (b \/ c) /\ (a \/ d) /\ (b \/ d) -> a /\ b \/ c /\ d.