用泛模态刻画团队逻辑的模态可定义性
Characterising Modal Definability of Team-Based Logics via the Universal Modality
摘要：
我们研究了各种模态逻辑的模型和框架可定义性。设ML（A+）表示用普适模态扩展的模态逻辑的片段，其中普适模态只肯定地出现。我们证明了一类Kripke模型在ML（A+）中是可定义的当且仅当该类是初等的，并且在不相交的工会和满射互模拟下是封闭的。我们还讨论了ML（A+）的可定义性的精神，著名的Goldblatt-Maxason定理。我们证明了Kripke框架的一个初等类F在ML（A+）中是可定义的当且仅当F在取生成子帧和有界形态图像下是闭的，并且反映了超滤子扩展和超滤子帧生成.此外，我们还研究了相对于有限传递框架的框架可定义性，并给出了相对于有限传递框架的ML（A+）-可定义性的一个类似刻画。最后，我们在团队逻辑中开始了模型和框架可定义性的研究。我们研究（扩展）模态依赖逻辑，（扩展）模态包含逻辑和模态团队逻辑。我们建立严格的线性层次模型的可定义性和框架的可定义性，分别。我们表明，关于模型和框架的可定义性，前面提到的团队为基础的逻辑，除了模态依赖逻辑，要么符合ML（A+）或平原模态逻辑ML。因此，作为一个推论，我们得到的模型和框架可定义的团队为基础的逻辑的模型论特征。
英文摘要：
We study model and frame definability of various modal logics. Let ML(A+) denote the fragment of modal logic extended with the universal modality in which the universal modality occurs only positively. We show that a class of Kripke models is definable in ML(A+) if and only if the class is elementary and closed under disjoint unions and surjective bisimulations. We also characterise the definability of ML(A+) in the spirit of the well-known Goldblatt--Thomason theorem. We show that an elementary class F of Kripke frames is definable in ML(A+) if and only if F is closed under taking generated subframes and bounded morphic images, and reflects ultrafilter extensions and finitely generated subframes. In addition we study frame definability relative to finite transitive frames and give an analogous characterisation of ML(A+)-definability relative to finite transitive frames. Finally, we initiate the study of model and frame definability in team-based logics. We study (extended) modal dependence logic, (extended) modal inclusion logic, and modal team logic. We establish strict linear hierarchies with respect to model definability and frame definability, respectively. We show that, with respect to model and frame definability, the before mentioned team-based logics, except modal dependence logic, either coincide with ML(A+) or plain modal logic ML. Thus as a corollary we obtain model theoretic characterisation of model and frame definability for the team-based logics.
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