Section logic2.
Context {L : Type}.
Context {ILO : ILogicOps L}.
Context {IL : ILogic L}.
Definition liff (A B : L) : L :=
(A -->> B) //\\ (B -->> A).
Local Notation "x <<-->> y" := (liff x y) (at level 78).

Lemma landA_ap : forall P Q R G,
(P //\\ Q) //\\ R |-- G ->
P //\\ Q //\\ R |-- G.