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9h
comment Counterexample on completely distributive lattices
In case it helps, I have written out a proof that completely distributive Boolean algebras are atomic, in the nLab here: ncatlab.org/nlab/show/…
17h
comment Fixed point theorems
@WłodzimierzHolsztyński The "question" asks for interesting examples of fixed point theorems, in the interest of compiling a big list.
21h
revised Counterexample on completely distributive lattices
a few more words of explanation
21h
answered Counterexample on completely distributive lattices
1d
awarded  Nice Answer
1d
revised A question about summation formula involving binomial coefficient
corrected a typo; slight rewording for more clarity
1d
comment Why are the integers with the cofinite topology not path-connected?
Well, you need something: any function from an interval to an indiscrete space is continuous, so indiscrete spaces are path-connected. They cannot be arc-connected if they are countable. That a path-connected Hausdorff space is arc-connected is a pretty non-trivial theorem.
2d
answered A question about summation formula involving binomial coefficient
2d
revised Is every frame monomorphism regular?
corrected a typo
2d
revised Is every frame monomorphism regular?
corrected a typo
2d
answered Is every frame monomorphism regular?
2d
answered Extremal, but not regular monomorphism
2d
revised inverted factorial and trailing zeros problem
tried fixing the link
Apr
14
comment How to integrate complex numbers?
This site is for professional mathematicians and their PhD students to discuss their research. Mathematical questions outside of that scope may be asked at math.stackexchange. However, the present question might be closed there too as it hasn't been expressed with much care -- it might be better to talk to your instructor or a teaching assistant.
Apr
13
awarded  Nice Answer
Apr
13
comment How many subspaces are generated by three or more subspaces in a Hilbert space?
That's because, I think, the general case is extremely hard. Even the case $n = 4$ is apparently really hard. One can obtain infinitely many subspaces from 4 subspaces in general position; see sciencedirect.com/science/article/pii/S0022404907000217 and Rota's article "Ten mathematics problems I will never solve" (behind paywall: degruyter.com/view/j/dmvm.1998.6.issue-2/dmvm-1998-0215/…).
Apr
13
comment Snake-like continua and universal images
@DavidWhite It's there by intention, as several recent discussions have borne out. Probably no one but the author understands why he type-sets that way, but I think it would be wise not to pursue this here and now. The mathematics looks interesting.
Apr
13
comment Answer to “why is matrix called matrix and what does it have to do with the movie?”
I have a feeling this will be considered off-topic. You might consider posting to History of Math and Science. But "matrix" comes from the Latin (ultimately deriving from mater, mother), and one should just look it up: Merriam online says "something within or from which something else originates, develops, or takes form". The movie meaning fits with that. The word as used in mathematics was introduced by Sylvester: en.wikipedia.org/wiki/Matrix_%28mathematics%29#History
Apr
12
comment k-linear abelian categories which are not categories of modules
I have a suspicion that something like chain complexes whose total space is finite-dimensional would be a counterexample, but I don't have time to look into it at the moment.
Apr
12
comment Can there be a non-trivial epimorphism (of rings) from a field?
@tj_ I expect what you mean is that $Tor$ commutes with filtered or directed colimits, not to be confused with direct limits = colimits. But your argument still goes through. And perhaps more to the point, I take it that you meant to offer a choice-free argument (I already knew modules over fields are flat assuming choice), and the argument seems valid in that respect as well. Thanks!