@prefix : <foo://bla/>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix owl: <http://www.w3.org/2002/07/owl#>.
:A rdf:type owl:Class.        :B rdf:type owl:Class.
:Union1 owl:equivalentClass [ owl:unionOf (:A :B) ].
:CompA owl:complementOf :A.   :CompB owl:complementOf :B.
:IntersectComps owl:equivalentClass [ owl:intersectionOf (:CompA :CompB)].
:Union2 owl:complementOf :IntersectComps.
:x rdf:type :A.               :x rdf:type :B.
:y rdf:type :CompA. # a negative assertion y not in A would be better -> OWL 2
:y rdf:type :CompB.