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6. Mathematics / B. Foundations for Mathematics / 5. Definitions of Number / f. Zermelo numbers

[Zermelo's view of numbers as nested sets]

3 ideas
For Zermelo the successor of n is {n} (rather than n U {n}) [Zermelo, by Maddy]
Zermelo's model of arithmetic is distinctive because it rests on a primitive of set theory [Lewis]
Two definitions of 3 in terms of sets disagree over whether 1 is a member of 3 [Shapiro]