On 14 January 2014 11:40, Stephen Paul King <stephe...@provensecure.com>wrote:

> A set whose proper subsets are isomorphic to the set.

Very nice definition, I knew that one (honest!) having read a book by Rudy
Rucker on the subject, but had forgotten it. This is the property nicely
illustrated by Hilbert's hotel.

One can define infinity in various ways if one assumes arithmetical
realism. One can only define it constructively if one assumes that
arithmetic is a human invention (but then one has to explain the
"unreasonable effectiveness" of maths).

The debate continues...although I must admit I thought you were on the
"constructivist" side, Mr K!?

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