Nam Nguyen wrote: > On 29/05/2013 3:25 AM, Peter Percival wrote: >> Nam Nguyen wrote: >> >>> >>> Well, then, why don't you express infinity with purely logical >>> symbols, for us all in the 2 fora to see? Seriously, that would >>> be a great achievement! >> >> It is easy enough to find formulae whose only models are infinite. > > Go ahead and write down one such formula that would express infinity > but has only logical symbols.
You know, don't you, that what a logical symbol is isn't definite. For example Abraham Robinson, in his books on model theory, doesn't include '='. Russell thought that he could express the axiom of infinity using logical symbols only.
-- I think I am an Elephant, Behind another Elephant Behind /another/ Elephant who isn't really there.... A.A. Milne