My research is focused on mathematical logic, and it has been primarily concerned with non-classical logics. My main areas of interest are as follows: (1) Many-valued logics and related algebras (fuzzy logics, residuated lattices, model theory of fuzzy logics), (2) Substructural logics with relational semantics (intuitionistic logic, relevant logic), and (3) Non-classical mathematics (mathematics done in a non-classical logical background).