A note on de re modalities
An extension of a result by \textit{G. E. Hughes} and \textit{M. J. Cresswell} [A new introduction to modal logic. Routledge, London (1996; Zbl 0855.03002)] is proved. Hughes and Cresswell showed that de re modalities are not eliminable in any system contained in S5. It is shown here that for every normal system S, except Triv, Ver and their intersection, de are modalities are not eliminable in \(\text{S}+ \text{BF}\).
scientific article; zbMATH DE number 1641320