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  1. Balder ten Cate, Gaëlle Fontaine & Tadeusz Litak (2010). Some Modal Aspects of XPath. Journal of Applied Non-Classical Logics 20 (3):139-171.
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  2. Tadeusz Litak & Frank Wolter (2005). All Finitely Axiomatizable Tense Logics of Linear Time Flows Are CoNP-Complete. Studia Logica 81 (2):153 - 165.
    We prove that all finitely axiomatizable tense logics with temporal operators for ‘always in the future’ and ‘always in the past’ and determined by linear fows time are coNP-complete. It follows, for example, that all tense logics containing a density axiom of the form ■n+1F p → nF p, for some n ≥ 0, are coNP-complete. Additionally, we prove coNP-completeness of all ∩-irreducible tense logics. As these classes of tense logics contain many Kripke incomplete bimodal logics, we obtain many natural (...)
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  3. Tadeusz Litak (2004). Modal Incompleteness Revisited. Studia Logica 76 (3):329 - 342.
    In this paper, we are going to analyze the phenomenon of modal incompleteness from an algebraic point of view. The usual method of showing that a given logic L is incomplete is to show that for some L and some cannot be separated from by a suitably wide class of complete algebras — usually Kripke algebras. We are going to show that classical examples of incomplete logics, e.g., Fine logic, are not complete with respect to any class of complete BAOs. (...)
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  4. Tadeusz Litak (2004). Some Notes on the Superintuitionistic Logic of Chequered Subsets of R∞. Bulletin of the Section of Logic 33 (2):81-86.
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