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19h

comment 
Algebra II exercise (help)
Sorry, this is a site for professional mathematicians. 
19h

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A question about Category Theory
Besides the objections made by quid and Peter: I don't think it's so much a question about category theory as it is about some theory (due to Solomon Feferman?) called "Unlimited Category Theory", which I've never heard of, and which almost sounds like it was invented in order to be refuted. Anyway, please consider changing the title. 
1d

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Is this permutationsum problem NPcomplete?
As a courtesy, one should always leave notes that one has crossposted, with links to all the relevant sites where the post appears. I see this has been done at this site in the body of the question. 
1d

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I discovered something, what do I do?
This question is outside the scope of this site, but if there is a university nearby, call or email the math department and ask if there is someone who would be willing to meet with you to discuss your discovery. It might help if you could tell them what area of math is involved so that a reasonable professor can be matched to your area. If a meeting can be arranged, my advice would be to go in very polite and humble and open, and try to realize that the odds are overwhelming that somebody already made that discovery. How hard have you tried to Google this? 
1d

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vector spaces with uncountable dimension and a nice basis
A very pretty way of exhibiting an explicit continuum size $\mathbb{Q}$linearly independent set of reals was given by François Dorais here: mathoverflow.net/a/23206/78711 
1d

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Category theory for Algebraic Geometry
Speaking as a category theorist, I think this is sound advice. As much as I like the book by Moerdijk and Mac Lane, I don't think it's required reading by any means; I'd learn category theory just on an asneeded basis (and if you like it and want to learn more, then consider looking into books by category theorists). Experts like Vakil can certainly guide you in how much you realistically need for AG. (There is also, of course, SGA which develops a ton of category theory ab initio, and which you will probably consult somewhere down the road.) 
Sep
1 
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A question on spectrum
Please consider asking at Mathematics StackExchange instead. (This smells like homework, which is typically not what we entertain here.) Be prepared in that case to explain to them what you have tried. 
Aug
31 
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Partitioning graph for Graph Isomorphism
Migrating to Theor. Comp. Sci. on request of OP... 
Aug
31 
revised 
Partitioning graph for Graph Isomorphism
cleaned up some of the grammar and orthography 
Aug
31 
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An exercise in the Kaplansky's book
Is it "D. Lizard", or "D. Lazard"? 
Aug
31 
revised 
Standard name / symbol for intersection in Brouwerian lattices
added what seemed a reasonable tag 
Aug
30 
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Making idempotent element by a relation
@KeithKearnes Thanks; that has the ring of truth to it. With that, closure seems completely justified. 
Aug
30 
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Is $\mathbb{R}^3 \setminus \mathbb{Q}^3$ simply connected?
@MikeMiller Why not write up the argument carefully as an answer before the question is closed? The comment as written is a little too telegraphic for me to follow easily, and I don't know which thing of Hirsch you mean. A careful, detailed, selfcontained answer would be peachy. 
Aug
30 
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Making idempotent element by a relation
There were four votes to close because of "unclear what you're asking". I thought it was clear, but a little too easy. 
Aug
30 
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Making idempotent element by a relation
Yes, but this doesn't answer the question, does it? Andreas's answer is that the only such idempotent is $1$. 
Aug
30 
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Is $\mathbb{R}^3 \setminus \mathbb{Q}^3$ simply connected?
While I harbor some doubts that one could do better than Martin's answer below, why not explain this alternative argument? It could be educational, even for professionals. 
Aug
29 
revised 
probability mass function fitting
removed iTunes gift card ad 
Aug
29 
revised 
probability mass function fitting
removed iTunes gift card ad 
Aug
29 
revised 
Awfully sophisticated proof for simple facts
hopefully the hole will be fixed 
Aug
29 
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Prime ideals decomposition
Crosspost: math.stackexchange.com/questions/1413527/… Read this: meta.stackexchange.com/questions/64068/… 