Lemma sound_andp_stable {L: Language} {minL: MinimunLanguage L} {pL: PropositionalLanguage L} {MD: Model} {kMD: KripkeModel MD} {M: Kmodel} {R: SS.Relation (Kworlds M)} {SM: Semantics L MD} {tpSM: TrivialPropositionalSemantics L MD SM} {stableSM: SemanticStable L MD M SM}: forall x y: expr, semantic_stable x -> semantic_stable y -> semantic_stable (x && y).