3,377 reputation
1837
bio website jakitoimgeisterhaus.blogspot.…
location Munich, Germany
age 38
visits member for 3 years, 6 months
seen 5 hours ago

My past research interests included differential algebraic equations, nonlinear analysis and relations between symmetries and structural properties.

I recently investigated hierarchical structures, starting from group cohomology, continuing with semi-group theory and ending with lattices and universal algebra.


Jul
29
revised Divergence transforms as scalar under rotation in 2D + intuition
Observed that a constant determinant is enough...
Jul
28
answered Divergence transforms as scalar under rotation in 2D + intuition
Jul
28
answered Divergence transforms as scalar under rotation in 2D + intuition
Jul
15
answered Is there an intuitive way to understand why a frequency cannot be writen as a sum of other frequencies?
Jul
14
comment Crankery: Is there a perfect inner model of ZFC?
@AndreasBlass I also noted that the "detailed requirements" for inner models imply that they are "proper classes". This is more than just a detail, because the model theory I have learned so far assumed the domain to be a set. It's not obvious to me how much this changes things, or how it is intended to be interpreted. I'm unsure whether this means that we are actually using NBG instead of ZFC (so that we can talk about proper classes), or whether it just means that there is another ZFC meta-universe, in which both the model and its inner model live. I will first have to work this out for me..
Jul
12
comment Crankery: Is there a perfect inner model of ZFC?
@AndreasBlass My intention was to use the notion of "inner model" in the usual sense. I was aware that there are additional requirements for inner models, like being transitive, but didn't look up all requirements in detail. The general intention of the question was to turn the statement from A. Sochor into a precise mathematical statement which can be analyzed with mathematical rigor.
Jul
1
asked Crankery: Is there a perfect inner model of ZFC?
Jun
23
awarded  Yearling
Jun
16
revised Decidability of the consistency for complete finitely axiomatized theories?
added 5 characters in body
Jun
16
revised Decidability of the consistency for complete finitely axiomatized theories?
added clarification about presentation of the problem to an algorithm to the question. This clarification turned out to be longer than the question itself...
Jun
16
answered Decidability of the consistency for complete finitely axiomatized theories?
Jun
15
comment What is the advantage and disadvantage of Hilbert System?
@DougSpoonwood While trying to find the answer to a question I recently asked, I also stumbled upon a paper claiming condensed detachment would allow to do without axiom schemes. I didn't read it in detail. However, the two axioms you propose look like axiom schemes to me. The $p$, $q$ and $r$ in your axioms are intended to be substituted with arbitrary formulas, hence these are two axiom schemes, not two single axioms. But I would be happy if you can explain it to me so I see that I'm wrong.
Jun
14
comment Decidability of the consistency for complete finitely axiomatized theories?
@boumol The reformulation is nearly adequate, except for the "(we can prove that)" part, where the initial question is a bit open anyway.
Jun
14
comment Decidability of the consistency for complete finitely axiomatized theories?
@PeterSmith OK, then I understand your point. So I will have to edit the question to make it clear that $\Phi$ is presented (to the algorithm which should decide its consistency) as the sequence of symbols which make up the first order formula $\varphi$ (which represents $\Phi$). But before I do this, I have to think about how the proof that $\phi$ is complete should be presented (to the algorithm). Maybe I will just omit the "(we can prove that)" part, even if this might open the door for simple counter examples.
Jun
14
comment Decidability of the consistency for complete finitely axiomatized theories?
Of course the question assumes that $\Phi$ is given explicitly. I'm not sure whether this answer is just nitpicking on the formulation of the question, or whether it is a "real" answer that I should try to understand (on a deeper level).
Jun
14
revised Decidability of the consistency for complete finitely axiomatized theories?
edited tags
Jun
14
answered What is the relationship between “recursive” or “recursively enumerable” sets and the concept of recursion?
Jun
13
asked Decidability of the consistency for complete finitely axiomatized theories?
Jun
10
answered Which set theories without the power set axiom are used occasionally?
Jun
9
answered Levenberg-Marquardt - Is forcing Hessian to be positive definite OK?