On 12/9/2012 2:49 AM, Virgil wrote: > In article > <firstname.lastname@example.org>, > WM <email@example.com> wrote: > >> On 9 Dez., 00:58, Virgil <vir...@ligriv.com> wrote: >> >>> A mathematical set only has to distinguish between elements and >>> non-elements, never between one of its element and another. >> >> A real number in mathematics has to be an individual that is distinct >> from every other real number. > > But no criterion for being in, or not in, the set of reals distinguishes > between any one real and any another real. > > So however relevant such differences may be for other purposes, as far > as any set containing them is concerned differences between members is > totally irrelevant. > > "Is x a member of y?" is a purely yes or no question. >
Only with respect to a well-construed universe of discourse.