It is unfortunate that we still tend to speak of "infinity" as a number. Suppose we spoke of its contrary as "finity". Then we would get stuff like:
finity + finity = finity
finity - finity = finity
finity*finity = finity
. Phooey on that! With discrimination between +ve infinity and -ve infinity, the situation only gets worse:
Is (+ve finity) + (-ve finity) equal to -ve finity, 0 or +ve finity?
Instead of infinities, I would prefer something like "transfinite numbers" as a class, but very individual and well-discriminated. Maybe there is even a better name (one lecturer at MIT tried "macho numbers", versus "wimps").
Alas, it is hard to undo centuries of habit!
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A comment on non-standard numbers: they are great for providing proofs of theorems, returning at the end to the original domain with only ordinary finite numbers. But trying to use non-standard numbers to produce results in an extended domain as the final result leaves us with a problem: there are pairs of non-standard numbers for which we can't tell their order:
In other words, we can't tell for some non-standard numbers x and y whether x < y, x=y or x > y. That is OK in the non-standard analysis usage, because those numbers don't occur in the final result. But if we want results in the extended system, then we are stuck.
But maybe someone has already found a constructible free hyperfilter or Lindstrom measure function and I don't know it. Happy thought!
