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1d
comment What is the most useful non-existing object of your field?
@AndréHenriques: Actually, it has $2^8$ elements. But you are correct that free complete Boolean algebras on finite sets exist (and are the same as free Boolean algebras). Free complete Boolean algebras on infinite sets do not exist.
1d
reviewed Looks OK What is the most useful non-existing object of your field?
Sep
23
comment A simple example of a ring that is an $A$-module but not an $A$-algebra?
I'm not sure why you say $\mathbb{R}$ is a $\mathbb{C}$-vector space but not a $\mathbb{C}$-algebra; any embedding of $\mathbb{C}$ in $\mathbb{R}$ makes $\mathbb{R}$ a $\mathbb{C}$-algebra. In your situation, $B$ will be an $A$-algebra iff the action of $A$ on $B$ commutes with the action of $B$ on itself. Equivalently, $B$ is an $A$-algebra iff the action of $a\in A$ coincides with multiplication by $a\cdot 1_B$ in the ring structure of $B$.
Sep
9
answered Completion of the set of subsets with half volume.
Sep
4
awarded  Enlightened
Sep
4
awarded  Nice Answer
Sep
3
answered Haar Measure on Locally Compact Semigroups
Sep
2
revised Is there a straightedge and compass construction of incommensurables in the hyperbolic plane?
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Sep
1
revised Group structure on an arbitrary completely regular topological space that makes $(x,y)\mapsto xy^{-1}$ continuous at $(1,1)$
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Aug
27
comment Clutching functions and Classifying maps
The clutching function correspondence gives you one way of constructing an equivalence $G\simeq \Omega BG$, and you are asking whether that equivalence is the same as the equivalence $G\simeq \Omega BG$. But this is impossible to answer without specifying how the latter equivalence is constructed.
Aug
24
comment Continuous relations?
@JoonasIlmavirta: That definition will give you closed relations, which are not very well-behaved other than being symmetric in $X$ and $Y$. They are not closed under composition and include functions that are not continuous as functions. If you replace $K$ by $Y$ (so you are looking locally only on $X$), you get my definition of continuity (since it is local on the domain).
Aug
24
awarded  gn.general-topology
Aug
23
revised Continuous relations?
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Aug
23
revised Continuous relations?
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Aug
23
revised Continuous relations?
previous edit was incorrect
Aug
23
revised Continuous relations?
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Aug
23
revised Continuous relations?
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Aug
23
revised Continuous relations?
added 47 characters in body
Aug
23
answered Continuous relations?
Aug
22
revised Continuous relations?
clarify what kind of "relation" is meant