[FOM] Hartogs' Lemma

[Alasdair Urquhart]

The original question raised by Thomas Forster
was whether Hartogs uses the Replacement Axiom
either explicitly or implicitly.  In fact,
he doesn't.  He invokes the Power Set and
Separation axioms explicitly in his proof.

There is an excellent discussion of Hartogs's
paper and its historical background in
Greg Moore's fine history "Zermelo's Axiom
of Choice: Its origins, development and influence,"
pp. 170-171.  Moore gives a very clear outline
of Hartogs's proof.