Section Pure.
Context {A : Type} {ILOPs : ILogicOps A} {BILOps : BILogicOps A}.
Class PureOp := {
pure : A -> Prop
}.
Definition parameter_pure (pure : A -> Prop) (P : A) : Prop :=
(forall Q, P //\\ Q |-- P ** Q) /\
(forall Q, pure Q -> P ** Q |-- P //\\ Q) /\
(forall Q R, (P //\\ Q) ** R -|- P //\\ (Q ** R)) /\
(forall Q, P -* Q |-- P -->> Q) /\
(forall Q, pure Q -> P -->> Q |-- P -* Q).
Class Pure {HP : PureOp} :=
{ pure_axiom : forall p, pure p -> parameter_pure pure p
; pure_proper : Proper (lequiv ==> iff) pure
}.
Existing Class pure.
Context (IL : ILogic A) (BIL : BILogic A) (po : PureOp) (p : @Pure po).

Lemma purescand  P Q : pure P -> pure Q -> P ** Q |-- P //\\ Q.