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math.LO2026
Interpolation above S4
Simon Santschi, Niels C. Vooijs
We complete Maksimova's classification of the normal extensions of S4 with interpolation. In particular, we prove Craig interpolation for the six extensions of S4 for which Craig i…
math.LO2024
Equational theories of idempotent semifields
George Metcalfe, Simon Santschi
This paper provides answers to several open problems about equational theories of idempotent semifields. In particular, it is proved that (i) no equational theory of a non-trivial…
math.LO2024
Interpolation in Hájek's Basic Logic
Wesley Fussner, Simon Santschi
We exhaustively classify varieties of BL-algebras with the amalgamation property, showing that there are only countably many of them and solving an open problem of Montagna. As a c…