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Formal aspects of various ways of description of Jan Łukasiewicz's four-valued modal logic £ are discussed. The original Łukasiewicz's description by means of the accepted and rejected theorems, together with the four-valued matrix, is presented. Then the improved E. J. Lemmon's description based upon three specific axioms, together with the relational semantics, is presented as well. It is proved that Lemmon's axiomatics is not independent: one axiom is derivable on the base of the remanentdoi:10.12775/llp.2011.012 fatcat:2tfdgf7pyze4re3w73hyuy3wm4