[OPE-L:7128] [OPE-L:630] Re: Re: Equality and Equivalence: Response requested

C. J. Arthur (cjarthur@pavilion.co.uk)
Tue, 9 Mar 1999 00:15:37 +0000

I am a week behind reading this torrent of mails but I risk intervening now:
Gil Skillman writes:
>(They go on to say (p. 28) that equality implies RST and it implies a
>substitution property Z (such as Alan's Axiom 4). But they never assert
>the converse, that RST plus Z imply equality, contrary to Alan's
My logic books do make this last inference. In Tarski it is called 'the
principle of abstraction' ; what I cannot quite figure out is if this means
we have here simply an abbreviated way of talking, or is it an inference to
some substanital property.
Chris Arthur