- ...Lemma
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Originally proved by K. Kuratowski (1923) and R.L. Moore (1923); this was rediscovered by M. Zorn in 1935, and credited to him by Bourbaki.
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- ...infinity)
- Later versions would use
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- ...cardinality),
- Zermelo did not used ordered pairs. He starts with disjoint A and B and considers the set M in
consisting of doubletons with exactly one element from each of A and B. Then he looks for R in M which provide a 1-1 correspondence.
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- ...integers
- Zermelo first looked at numbers in later articles.
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- ...sets.
- Fraenkel published similar observations the same year.
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- ...(ZFC)
- For a leisurely treatment, i.e., in the spirit of Zermelo's original paper, see Halmos' Naive Set Theory.
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