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visits member for 4 years, 10 months
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Just when I thought I was out, they pull me back in


1d
comment Are there other nice math books close to the style of Tristan Needham?
I'm sure it's a good book, but that is not what this question is asking for
2d
comment biproduct and tensorial product
Just to further emphasise @JamesCranch's comment: even at the level of counting rank (or, if we're using vector spaces as our category, counting dimension) the claimed objects clearly don't match: $(j+k)\times m \neq j\times (k+m)$
2d
comment Invertible operator with countable spectrum
@JoonasIlmavirta yes, my confusion was precisely this difference of terminology. But I am fairly sure the OP uses my definition of "invertible"
Aug
24
reviewed Leave Open Existence of finite nonabelian groups satisfying certain identities
Aug
24
comment Invertible operator with countable spectrum
@JoonasIlmavirta My confusion is: you said above "The inverse of a bounded invertible operator need not be bounded" and the Banach isomorphism theorem tells us that actually, this is always the case
Aug
24
comment Invertible operator with countable spectrum
@JoonasIlmavirta I don't understand your comment about inverses, unless you are dealing with densely-defined operators. In the case of bounded operators on a Banach space we have the Banach isomorphism theorem, unless I have misread or misunderstood something
Aug
23
comment A example on Fourier tranform of a continous compactly supported function
Doesn't this run into problems in view of the following form of the uncertainty principle? en.wikipedia.org/wiki/Uncertainty_principle#Harmonic_analysis
Aug
22
reviewed Approve suggested edit on A lifting problem
Aug
22
reviewed Reject suggested edit on Operator norm vs spectral radius for positive matrices
Aug
22
comment Operator norm vs spectral radius for positive matrices
@abx I think that for those of us who grew up reading formulas typed in raw form and who wish to avoid the page jerking as loads of MathJax crunches, it is not such a big ideal. But I am prepared to accept I am in the minority
Aug
22
reviewed Leave Open A group allowing exactly 7 group topologies
Aug
21
reviewed Approve suggested edit on abstract-polytopes tag wiki excerpt
Aug
20
reviewed Close Examples of etale group schemes
Aug
20
reviewed Leave Open Automorphism group of a smooth quadric $Q\subset\mathbb{P}^4$
Aug
20
reviewed Leave Open Can a lower-order trigonometric polynomials fit the data generated by a higher-order one?
Aug
20
comment Where to find (personal) motivation
I advise my friends as my friends. I don't see the point in attempting to offer "agony aunt" advice from a distance without any knowledge of the underlying causes or motives
Aug
19
reviewed Reopen Problem of book Kunen
Aug
19
reviewed Reopen How to prove a Proposition of Rouquier?
Aug
18
comment Interpretation of Hochschild Homology groups
OK, probably I have misremembered. I know he does 1st and 2nd degree cohomology.
Aug
17
reviewed Reject suggested edit on Are there two non-homotopy equivalent spaces with equal homotopy groups?