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[parent] example of infinite hyperreal number (Example)

The hyperreal number $\{n\}_{n \in \mathbb{N}}\; \in {}^*\mathbb{R}\;$ is infinite (or unlimited).

Proof : Let $\mathcal{F}$ be the nonprincipal ultrafilter fixed in the parent entry.

Given any positive $a \in \mathbb{R}$ we have that $\{n \in \mathbb{N} : n \leq a\}$ is finite, so $\{n \in \mathbb{N} : a < n\} \in \mathcal{F}$ and therefore $\{a\}_{n \in \mathbb{N}} < \{n\}_{n \in \mathbb{N}}$

Thus $\{n\}_{n \in \mathbb{N}}$ is infinite.$\square$




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Cross-references: infinite, finite, positive, nonprincipal ultrafilter, proof, number, hyperreal

This is version 2 of example of infinite hyperreal number, born on 2007-07-28, modified 2007-07-28.
Object id is 9809, canonical name is ExampleOfInfiniteHyperrealNumber.
Accessed 659 times total.

Classification:
AMS MSC26E35 (Real functions :: Miscellaneous topics :: Nonstandard analysis)

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