A relation algebraic approach to modal correspondences - Wolfgang Heinle (Forschungsberichte, TU Munich, 1991)

Expressivity and definability in extended modal languages. - Wolfgang Heinle (Shaker, 1995)

Relation Algebra and Modal Logics. - Holger Schlingloff; Wolfgang Heinle (Relational Methods in Computer Science, 1997)

Relations Between Propositional Normal Modal Logics: An Overview. - Rajeev Goré; Wolfgang Heinle; Alain Heuerding (J. Log. Comput., 1997)