414 reputation
28
bio website
location
age
visits member for 2 years, 2 months
seen Feb 26 at 5:32

Feb
21
comment Homology isomorphism of $H_n(S^d\times X)$ and $H_{n-1}(S^{d-1}\times X)$
Thanks. Maybe I made a mistake copying the statement.
Dec
20
comment $cov(null)$ in a Cohen model
Thanks, I will look at that.
Dec
19
comment $cov(null)$ in a Cohen model
Could you point me where to find a proof of this?
Dec
17
comment $cov(null)$ in a Cohen model
But what about CH in the ground model, is that not necessary for the (general) statement?
Dec
17
comment $cov(null)$ in a Cohen model
Why is this better?
Jul
21
comment About singular $\beth_{\alpha}$ for limit ordinals $\alpha$
math.uni-bonn.de/people/logic/teaching/2013SS/… page 65, near the top, under "Case 2"
Jul
21
comment $H(\kappa)$-absoluteness of a formula
I think I fixed everything now.
Jul
21
comment $H(\kappa)$-absoluteness of a formula
Alright, thank you for your answers.
Jul
20
comment $H(\kappa)$-absoluteness of a formula
I see this shouldn't work because it would let ZFC prove its consistency, but I don't see the mistake in the argument at the moment.
Jul
20
comment $H(\kappa)$-absoluteness of a formula
I have a question regarding "cannot form elementary substructure of V", if you don't mind. Trying to form a Skolem hull for a set $X$, if there is $x\in V$ with $\varphi(x,y_1,..,y_k)$ for $y_i\in X$, choose $\alpha$ so that x is in $V_{\alpha}$. Since X is a set, there is $\alpha$ so that this works for all $\varphi$ and parameters in $X$ at the same time. Then wellorder $V_{\alpha}$ and choose the smallest element for each such $\varphi$, $y_i$. Take $X_1$ as the set of those elements. Repeat this, get sets $X_i\subset X_{i+1}$, the union ($i<\omega$) should be an elem. substructure of V.
Jul
20
comment $H(\kappa)$-absoluteness of a formula
I just realized I made a mistake in the question. $\varphi$ should be absolute between models of ZF minus powerset (which includes $H(\kappa)$ for uncountable $\kappa$). Also, $\kappa$ should indeed be uncountable regular. Sorry for all that.
Jul
20
comment $H(\kappa)$-absoluteness of a formula
No, $\kappa$ is arbitrary.
Jul
20
comment $H(\kappa)$-absoluteness of a formula
This means that, for any $y\in H(\kappa)$, $\psi(y)$ holds in V iff it holds in $H(\kappa)$. So in this case the task is to show that $x$ can be chosen in $H(\kappa)$ if such a x exists in V.
Jun
29
comment Definiteness of omega
If 0 is not a limit, then $Lim(y)\rightarrow y=0$ is equivalent to $\neg Lim(y)$ by the way. :)
Jun
29
comment Definiteness of omega
Yes, M is supposed to be transitive. Will edit..
May
28
comment ZF: Regularity axiom or axiom schema?
Thanks for the answer.
Apr
5
comment Existence of a singleton set (AC for a singleton set)
No, you read the question wrong. I don't want the existence of $\{x\}$, but of a $\{v\}$ for $v\in x$.
Feb
3
comment Definabilty of two functions on natural numbers
Oh, alright. I have to read into that..
Feb
2
comment polar decomposition for non square matrices
I think it should be $Px\mapsto Ax$ on $ran(P)$. Is that correct? Thanks for the answer.
Feb
2
comment polar decomposition for non square matrices
Fixed, thank you.