An admissibility criterion for inference rules with metavariables in the modal logic S4 · α N . Rutskij, A.N. — 2007 Sibirskij Matematicheskij Zhurnal
An inheritance criterion for the admissible inference rules of K4. Rutskij, A.N.; Fedorishin, B.R. — 2002 Sibirskij Matematicheskij Zhurnal