engleski

A note on normal form for closed fragment of system IL

P. Hajek and V. Svejdar determined normal forms for the system ILF, and showed that we can eliminate the modal operator $\rhd$ from IL-formulas. The normal form for the closed fragment of the interpretability logic IL is an open problem. We prove that we can eliminate the modal operator $\rhd$ in some cases. We give an example where it is impossible to eliminate $\rhd.$

modal logic ; interpretability logic ; normal form

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