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7h
comment A better proof for the set of irrational number not closed under ordinary multiplication.
"Weakened". Nice detail haha +1
14h
awarded  Cleanup
14h
revised A better proof for the set of irrational number not closed under ordinary multiplication.
rolled back to a previous revision
15h
comment A better proof for the set of irrational number not closed under ordinary multiplication.
@user222031 : Some elementary textbooks that introduce logic, combinatorics and set theory do use the bar to denote complements, but this is not standard notation in any analysis/algebra textbook since it leads to confusing with many closure operators (the topological closure in analysis, integral closure / algebraic closure in ring theory, etc.). Instead we use $\backslash$ or $-$. Although I am not sure about modern logic theory/model theory/set theory text books because I haven't read many of them.
15h
answered A better proof for the set of irrational number not closed under ordinary multiplication.
May
17
awarded  Notable Question
May
17
comment Question including Function and Radical
The downvotes on a new user are totally useless...
May
17
comment Question including Function and Radical
@Eff : That would be my first guess too, but then again, what does she want in the table? I don't know, a table could be a lot of things. It's also a question so that she learns to make clear questions :P
May
17
answered Question including Function and Radical
May
16
comment A random walk question: what is the given probability?
This. +1 en.wikipedia.org/wiki/Catalan_number#/media/…
May
16
comment A random walk question: what is the given probability?
@Aprilius : Are you claiming that you have an explicit formula for the answer and you're giving hints about it, or you're just trying to help? Because I've been computing a bit and I don't see this going anywhere, but then again I haven't done probability in a while.
May
16
revised A random walk question: what is the given probability?
added 12 characters in body
May
16
revised Pullback of box products of invertible sheaves
added 413 characters in body
May
16
awarded  limits
May
14
asked Pullback of box products of invertible sheaves
May
12
revised Is there anything to prove in this corollary?
edited title
May
11
comment Can the integers be made into a vector space over any Finite Field?
Then $\mathbb Z$ has what? Do you mean $\mathbb Z$ is a direct sum of a family of subgroups, i.e. the decomposition over a basis? Either way this answer is not very clear.
May
11
comment Why can't differentiability be generalized as nicely as continuity?
@Daniel McLaury : I think my answer made that point clearly enough, but I assume the OP was confused with the algebra at the beginning and focused on figuring it out, algebraic geometers will probably not learn much from this answer anyway!
May
11
comment Why can't differentiability be generalized as nicely as continuity?
@Daniel McLaury : But we don't get anything new in the context of differential geometry! The point is that in the case of a manifold, we don't get around patches, but a generalization does exist, so we do get something new, it's just not "differential geometry" new.
May
11
answered What does actually probability mean?