Combining Texts

Ideas for 'fragments/reports', 'Reference and Essence (1st edn)' and 'works'

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3 ideas

4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5
S4, and therefore S5, are invalid for metaphysical modality [Salmon,N, by Williamson]
4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / a. Axioms for sets
Zermelo made 'set' and 'member' undefined axioms [Zermelo, by Chihara]
For Zermelo's set theory the empty set is zero and the successor of each number is its unit set [Zermelo, by Blackburn]