 The method of  fusion  of modal logics (introduced in Thomason 1984) was developed with the idea of combining relation-based (hence normal) modal logics in both a syntactic way (by putting together their respective Hilbert-style axiom systems) and a semantic way (by taking the relations corresponding to the modality of each system, and putting them together in a single  model).[13]  Although the fusion of modal systems is fairly simple, the transference results that guarantee that properties are preserved (e.g., whether the combination of the sound and complete axiomatization of the existing systems is indeed sound and complete for the resulting one) are not straightforward (see, e.g., Kracht &amp; Wolter 1991, 1997; Fine &amp; Schurz 1996; Schurz 2011).