ML-1992-02: Skvortsov, Dmitrij P. and Shehtman, Valentin B. (1992) Maximal Kripke-type Semantics for Modal and Superintuitionistic Predicate Logics. [Report]
ML-1992-06: Gabbay, D.M. and Shehtman, Valentin B. (1992) Undecidability of Modal and Intermediate First-Order Logics with Two Individual Variables. [Report]