In this paper, we consider some versions of Fitting's L-valued logic and L-valued modal logic for a finite distributive lattice L. Using the theory of natural dualities, we first obtain a natural duality for algebras of L-valued logic (i.e., L-VL-algebras), which extends Stone duality for Boolean algebras to the L-valued case. Then, based on this duality, we develop a Jonsson-Tarski-style duality for algebras of L-valued modal logic (i.e., L-ML-algebras), which extends Jonsson-Tarski duality for modal algebras to the L-valued case. By applying these dualities, we obtain compactness theorems for L-valued logic and for L-valued modal logic, and the classification of equivalence classes of categories of L-VL-algebras for finite distributive lattices L.
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