(=> (Facet ?Relation) (Forall (?Tuple) (=> (Member ?Tuple ?Relation) (Triple ?Tuple)))) (=> (Facet ?Relation) (Not (Empty ?Relation))) (=> (Facet ?Relation) (= (Arity ?Relation) 3))
(<=> (Facet ?Relation) (And (Relation ?Relation) (Not (Empty ?Relation)) (Forall (?Tuple) (=> (Member ?Tuple ?Relation) (Triple ?Tuple)))))