Definition wk_split {A} {JA: Join A} :=
forall a b c d e : A, join a b c -> join d e c -> joins a d -> join_sub d b.

Lemma sepcon_andp_prop2 {A} {JA: Join A}{PA: Perm_alg A}{AG: ageable A}{XA: Age_alg A}:
forall P Q R,  (P * (!!Q && R) = !!Q && (P * R))%pred.