In article <firstname.lastname@example.org>, WM <email@example.com> wrote:
> On 3 Jun., 04:25, "Dik T. Winter" <Dik.Win...@cwi.nl> wrote: > > There is no difference between finite unions and infinite > > unions. > > There should not be, but there is --- at least if ZF is taken to be > true. > The union of FISONs (of natural numbers or of other finite linear > sets) is the last FISON.
If WM claims the existence of a last FISON, let him present it to us.
But outside of WM's U.N. Realistic world, every FISON is a proper subset of another FISON, so that the union of all of them cannot itself be one of them.
Or does WM's set theory require existence of sets which are proper subsets of themselves?