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Sep
17
reviewed Approve suggested edit on Is there a dense subset of the real plane with all pairwise distances rational?
Sep
10
awarded  Good Question
Aug
28
reviewed Reject suggested edit on Defining a topology in the Power Set
Aug
7
awarded  Tag Editor
Aug
7
revised conjectures wiki description
added 3 characters in body
Aug
7
suggested suggested edit on conjectures tag wiki
Jul
30
awarded  Nice Answer
Jul
22
reviewed Approve suggested edit on Solve this functional equation with respect to $f$
Jul
22
comment Proof correctness problem
There is a big list for question 2: mathoverflow.net/questions/35468/…
Jul
20
reviewed Approve suggested edit on Derivatives of infinite order
Jul
19
awarded  Nice Question
Jul
18
answered Proof correctness problem
Jul
17
comment Extremely messy proofs
Well, it's a paper of 30 pages. The relevant definitions and the actual proof are given on pages 4-19 which contain spacious diagrams and not too much text and additional examples on D-modules which can be skipped. Also it is so nicely written that you would rather want to last it longer :-)
Jul
2
awarded  Curious
Jul
1
awarded  Good Answer
Jun
13
comment Merging / combining categories
@user52856 The combination of several structures is category theoretically best handled by looking at internal versions of the structures in question. Topological groups are group objects in Top. Group objects can be seen as product preserving functors from a small category, the Lawvere theory of groups, or from an even smaller product sketch. Combination of first order structures can be nicely described in the language of sketches: There is a tensor product of sketches such that a model of $A \otimes B$ is the same as a model of $A$ in the category of models of $B$...
Jun
11
comment Merging / combining categories
An object in the pullback (strict or weak) in CAT of Top->Set<-Grp ist a set with a topology and a group structure. Nothing ensures that the structure maps of the group are continuous. Same with the required compatibilities in your other examples, e.g. if you try to present Rng as the pullback of Grp->Set<-Monoid you won't get a distributive law...
May
29
comment What are the connections between pi and prime numbers?
It shows up when one considers the infinite prime together with the usual primes: mathoverflow.net/q/7656/733
May
24
reviewed Approve suggested edit on Are all counterexamples of OEIS A226181 both Poulet numbers and Proth numbers?
Mar
31
reviewed Edit suggested edit on Is there a purely group-theoretic reformulation of an equivalence of subgroups?