Hint Resolve @subp_unfash.

(* Specifications: *)
Lemma unfash_sepcon_distrib:
forall {T}{agT: ageable T}{JoinT: Join T}{PermT: Perm_alg T}{SepT: Sep_alg T}{AgeT: Age_alg T}
(P: pred nat) (Q R: pred T),
unfash P && (Q*R) = (unfash P && Q) * (unfash P && R).