[FOM] Some historical questions
Thomas Forster
T.Forster at dpmms.cam.ac.uk
Sat Nov 6 05:02:49 EDT 2010
Allen Hazen and i have been in correspondence of late and some historical
questions have come up, which members of the list might be able to help us
with.
It's known that Hartogs' theorem can be proved without any use of
replacement. Did Hartogs' do it without any replacement? We know
replacement wasn't spelled out as an axiom in 1915 but he might have
use it cryptically anyway. Does anyone on this list know? Does anyone
have electronic copy of the original? Or of a translation into english
(or even french!)?
Paul Henrard has a clever way of defining equinumerosity between sets that
doesn't use ordered pairs, by using overlapping unordered pairs. Some
time in the 1970s. I don't *think* he ever published it. Allen Hazen
independently discovered (essentially) the same trick. Others may have
done the same. Does anyone know anywhere where such a gadget is
published? It would be good to get the history right.
tf
URL: www.dpmms.cam.ac.uk/~tf; DPMMS ph: +44-1223-337981;
(UEA ph: +44-1603-593588; mobile in UK +44-7887-701-562;)
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