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Continuum theory, point-set topology, spaces with algebraic structure, foundations, dimension theory, local and global properties.

3 votes
1 answer
502 views

Can Tychonoff's theorem be applied to topological spaces generated by program output in ZFC?

I am confused about an issue in set theory. Tychonoff's theorem says that "an arbitrary product of compact topological spaces is compact". We often talk of an index set $I$ and then for each $n\in I$ …
107 votes
9 answers
36k views

solving $f(f(x))=g(x)$

This question is of course inspired by the question How to solve f(f(x))=cosx and Joel David Hamkins' answer, which somehow gives a formal trick for solving equations of the form $f(f(x))=g(x)$ on a b …
9 votes
1 answer
285 views

Reference request: filter tends to filter along map

Recall that a filter on a set $X$ is a nonempty collection $\mathcal{F}$ of subsets of $X$ such that (i) $U\subseteq V\subseteq X$ and $U\in\mathcal{F}$ implies $V\in\mathcal{F}$, and (ii) $U,V\in\m …
29 votes
Accepted

Why are topological ideas so important in arithmetic?

Why are topological ideas so important in arithmetic? In some sense KConrad is of course spot on, but let me offer a completely different kind of answer. Why are complex functions of one variable so …
Kevin Buzzard's user avatar