### Ideas from 'Investigations in the Foundations of Set Theory I' by Ernst Zermelo , by Theme Structure

#### [found in 'From Frege to Gödel 1879-1931' (ed/tr Heijenoort,Jean van) [Harvard 1967,0-674-32449-8]].

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###### 2. Reason / D. Definition / 8. Impredicative Definition
 15924 Predicative definitions are acceptable in mathematics if they distinguish objects, rather than creating them? [Lavine]
###### 4. Formal Logic / F. Set Theory ST / 1. Set Theory
 17608 We take set theory as given, and retain everything valuable, while avoiding contradictions
 17607 Set theory investigates number, order and function, showing logical foundations for mathematics
###### 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / a. Axioms for sets
 10870 ZFC: Existence, Extension, Specification, Pairing, Unions, Powers, Infinity, Choice [Clegg]
 13012 Zermelo published his axioms in 1908, to secure a controversial proof [Maddy]
 17609 Set theory can be reduced to a few definitions and seven independent axioms
###### 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / c. Axiom of Pairing II
 13017 Zermelo introduced Pairing in 1930, and it seems fairly obvious [Maddy]
###### 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / i. Axiom of Foundation VIII
 13015 Zermelo used Foundation to block paradox, but then decided that only Separation was needed [Maddy]
###### 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / m. Axiom of Separation
 13020 The Axiom of Separation requires set generation up to one step back from contradiction [Maddy]
 13486 Not every predicate has an extension, but Separation picks the members that satisfy a predicate [Hart,WD]
###### 6. Mathematics / A. Nature of Mathematics / 3. Nature of Numbers / e. Ordinal numbers
 13487 In ZF, the Burali-Forti Paradox proves that there is no set of all ordinals [Hart,WD]
###### 6. Mathematics / B. Foundations for Mathematics / 5. Definitions of Number / f. Zermelo numbers
 18178 For Zermelo the successor of n is {n} (rather than n U {n}) [Maddy]
###### 6. Mathematics / B. Foundations for Mathematics / 6. Mathematics as Set Theory / a. Mathematics is set theory
 13027 Zermelo believed, and Von Neumann seemed to confirm, that numbers are sets [Maddy]
###### 6. Mathematics / B. Foundations for Mathematics / 7. Mathematical Structuralism / e. Structuralism critique
 9627 Different versions of set theory result in different underlying structures for numbers [Brown,JR]