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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 denselydefined 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 abstractpolytopes 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 lowerorder trigonometric polynomials fit the data generated by a higherorder 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 nonhomotopy equivalent spaces with equal homotopy groups? 