From: Nick Bostrom (bostrom@mail.ndirect.co.uk)
Date: Mon Nov 17 1997 - 16:44:45 MST
John K Clark wrote:
> If A is an infinite number then A -A = A not zero, A+A = A too, and A*A =A,
> but 2^A is not equal to A, it's a higher infinity.
Actually, it is not true that A-A=A for infinite cardinals A.
Sums involving positive and negative Cantorian infinities are not
defined. Robinsonian infinimal hyperreals do have addition defined
on them, but there I+(-I)=0. (It's because John's posts are usually
so accurate and correct that it is worth picking on small things like
this.)
Nick Bostrom
http://www.hedweb.com/nickb
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