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arXiv 2006.05396cs.LO
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非迭代模态逻辑是余代数的

Non-iterative Modal Logics are Coalgebraic

Jonas Forster, Lutz Schröder

摘要:

模态逻辑是\emph{non-iterative},如果它可以由不嵌套模态运算符的公理定义,并且\emph{rank-1},如果公理中的所有命题变量都在模态运算符的范围内。众所周知,每一个语法定义的秩-1模态逻辑可以配备一个规范的共代数语义,确保可靠性和强完备性。在目前的工作中,我们将这一结果扩展到非迭代模态逻辑,表明每一个非迭代模态逻辑可以配备一个规范的coalgebraic语义定义的copointed函子,再次确保健全性和强完备性,通过一个规范的模型建设。在秩1的情况下,典型的余代数语义等价于具有适当框架条件的邻域语义,因此邻域语义上的非迭代模态逻辑的强完备性是已知的。作为这些结果的一个例子,我们讨论道义逻辑与事实分离,这是捕获的公理是非迭代的,但不是秩~1。

英文摘要:

A modal logic is \emph{non-iterative} if it can be defined by axioms that do not nest modal operators, and \emph{rank-1} if additionally all propositional variables in axioms are in scope of a modal operator. It is known that every syntactically defined rank-1 modal logic can be equipped with a canonical coalgebraic semantics, ensuring soundness and strong completeness. In the present work, we extend this result to non-iterative modal logics, showing that every non-iterative modal logic can be equipped with a canonical coalgebraic semantics defined in terms of a copointed functor, again ensuring soundness and strong completeness via a canonical model construction. Like in the rank-1 case, the canonical coalgebraic semantics is equivalent to a neighbourhood semantics with suitable frame conditions, so the known strong completeness of non-iterative modal logics over neighbourhood semantics is implied. As an illustration of these results, we discuss deontic logics with factual detachment, which is captured by axioms that are non-iterative but not rank~1.

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