bio | website | tuwien.ac.at/goldstern |
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location | ||
age | ||
visits | member for | 4 years, 3 months |
seen | Aug 27 at 9:41 | |
stats | profile views | 2,715 |
Aug
13 |
comment |
Reconstructing relations with the image relation of a topology
@EricWofsey @ Joel Right. |
Aug
12 |
comment |
Reconstructing relations with the image relation of a topology
If $R$ is an equivalenc relation on an arbitrary set, can't you just put a well-order on the classes, and repeat your argument? "$f$ must take the least class to itself, and so on, now transfinitely"? |
Aug
12 |
comment |
Reconstructing relations with the image relation of a topology
I assume you want your pre-order to be linear (or "total"). |
Aug
12 |
comment |
Hausdorff spaces with asymmetric image relation
Of course! Thank you. |
Aug
12 |
answered | Hausdorff spaces with asymmetric image relation |
Aug
11 |
comment |
“Universal” connected spaces
$\kappa+1$ usually means $\kappa\cup \{\kappa\}$, or in order theoretic terms: the order of $\kappa$ (viewed as an ordinal), extended by an additional top element. |
Aug
5 |
comment |
A question on the name of a property
@FrodeBjørdal Rather than quoting my own book I can point to Shoenfield's book (4.2, page 45), which uses this notation. (But requires constants, not just any terms.) Also Hinman (Fundamentals of Math.Logic 3.1, page 196) calls a complete theory "Henkin complete" if there are "Henkin witnesses" for every closed existential formula. This concept is used for Henkin's proof of Gödel's completeness theorem. |
Aug
4 |
comment |
A question on the name of a property
If you require this property only for closed formulas of the form $\exists x\, F(x)$, then I would call $T$ a Henkin theory. |
Jul
30 |
answered | A group topology which commutes with closed subgroups |
Jul
29 |
comment |
Does a continuous map $f$ from the $n$-ball $B$ into $R^n$ such that $B\subset f(B)$ have a fixed point?
The new answer is even nicer than mine. |
Jul
28 |
revised |
Online introduction to Lattice Theory?
not to be confused: number theory, universal algebra |
Jul
23 |
comment |
Löwenheim-Skolem for many-sorted theories
Consider the two-sorted theory of "sets" and "elements". If your theory contains the extensionality axiom, then any model with $\kappa$ many "elements" has at most $2^\kappa$ many "sets". -- This can be iterated finitely many times. |
Jul
22 |
comment |
Contracting join-incomplete lattice endomorphisms
You use $f$ both for the given homomorphism and for the one you are looking for. Please call one of them $g$. |
Jul
15 |
comment |
Why is the set-theoretic principle $\diamondsuit$ called $\diamondsuit$?
@JoelDavidHamkins Just a stupid joke. The two halves of the diamond look like two-dimensional corner reflectors (en.wikipedia.org/wiki/Corner_reflector), so one reflects downwards, the other upwards. |
Jul
14 |
accepted | Why is the set-theoretic principle $\diamondsuit$ called $\diamondsuit$? |
Jul
14 |
comment |
Why is the set-theoretic principle $\diamondsuit$ called $\diamondsuit$?
@JoelDavidHamkins So $\curlyvee$ and $\curlywedge$ stand for upward and downward reflection? |
Jul
13 |
answered | Does a continuous map $f$ from the $n$-ball $B$ into $R^n$ such that $B\subset f(B)$ have a fixed point? |
Jul
13 |
asked | Why is the set-theoretic principle $\diamondsuit$ called $\diamondsuit$? |
Jul
8 |
answered | Incomplete lattice homomorphisms between complete lattices |
Jun
27 |
revised |
Preserving $\omega_1$ is Inaccessible to the reals
typos corrected: Schindler |