Setting the Basis for Here and There Modal Logics

International audienceWe define and study a new modal extension of the logic of Here and There with operators from modal logic K. We provide a complete axiomatisation together with several results such as the non-interdefinability of modal operators, the Hennessy-Milner and the finite model properties, a bound for the complexity of the related satisfiability problem and a discussion about the canonicity of some well-known Sahlqvist formulas in our setting. We also consider the equilibrium property on this logic and we prove the theorem of strong equivalence in the resulting framework