Combining Texts

All the ideas for 'Set Theory and related topics (2nd ed)', 'Elucidation of some points in E.Schrder' and 'A Completeness Theorem in Modal Logic'

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6 ideas

4. Formal Logic / D. Modal Logic ML / 1. Modal Logic
10163 Propositional modal logic has been proved to be complete [Kripke, by Feferman/Feferman]
4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / a. Systems of modal logic
10760 With possible worlds, S4 and S5 are sound and complete, but S1-S3 are not even sound [Kripke, by Rossberg]
4. Formal Logic / D. Modal Logic ML / 7. Barcan Formula
16189 The variable domain approach to quantified modal logic invalidates the Barcan Formula [Kripke, by Simchen]
15132 The Barcan formulas fail in models with varying domains [Kripke, by Williamson]
4. Formal Logic / F. Set Theory ST / 3. Types of Set / b. Empty (Null) Set
14238 A class is an aggregate of objects; if you destroy them, you destroy the class; there is no empty class [Frege]
4. Formal Logic / F. Set Theory ST / 3. Types of Set / e. Equivalence classes
8920 Equivalence relations are reflexive, symmetric and transitive, and classify similar objects [Lipschutz]