4,413 reputation
1033
bio website
location Scotland
age 32
visits member for 2 years, 9 months
seen 11 hours ago

I do research on groups, semigroups, and especially interactions between algebra and formal language theory. My non-research interests include combinatorics, elementary number theory and topology.


Oct
14
comment Is this induction proof correct?
As you have written it, $P(n)$ is not a statement, so it can't be true or false. (See Thomas's answer for how to fix this.)
Sep
30
awarded  Explainer
Sep
25
comment Difference between not both and both not and either or and neither nor
Yes. $\hspace{1cm}$
Sep
25
answered Difference between not both and both not and either or and neither nor
Sep
25
comment Complicated proof in Transformation Semigroups.
@nameless: I noticed you haven't accepted answers to any of your questions yet. It's nice that you thank the people who answer your questions, but also to help with the way this site is supposed to work, please accept answers by clicking on the 'tick' next to them.
Sep
24
awarded  Autobiographer
Mar
1
awarded  Yearling
Mar
1
awarded  Nice Answer
Jan
13
reviewed Approve suggested edit on Why - not how - do you solve Differential Equations?
Dec
19
revised What exactly are eigen-things?
deleted 6 characters in body
Aug
13
reviewed No Action Needed How do I find out the coordinates, interpolating across an angled line?
Jul
28
revised Structure theorem for finitely generated commutative $semi$groups.
Changed 'Tasmura' to 'Tamura' (I know one-letter edits are generally discouraged, but this seemed significant).
Jul
20
comment Mathematical writing: why should we not use the phrase “we have that”?
@ShreevatsaR: It's not just you, although I phrase things slightly differently, for example "We have $A=B$" I would read as "We have $A$ equal to $B$".
Jul
5
revised Whether $L=\{(a^m,a^n)\}^*$ is regular or not?
edited tags; edited title
Jul
4
comment Formal grammar for the language $L = \{w\in\{a,b\}^*,\,w=xx,\,x=a^nb^na^mb^m,\,n\ge0,\,m\ge0\}$
@Harald: Indeed this language isn't context-free. Probably it's easier to prove in this special case, but a generalisation is contained in my paper on poly-context-free groups (Theorem 3.12: the language $L$ in this question is essentially what I am calling $L^{(2,2)}$ - defined on p.19).
Jul
4
answered Whether $L=\{(a^m,a^n)\}^*$ is regular or not?
Jul
4
comment Whether $L=\{(a^m,a^n)\}^*$ is regular or not?
@Rudong: Your question still doesn't make sense. $L$ cannot be a regular language if you consider it as a 'language' over $A^*\times A^*$, because, as Boris has already pointed out, $A^*\times A^*$ is not a finite set.
May
26
answered Size of the image (rank) in $T_n$
May
26
revised Semigroup with exactly one left(right) identity?
specified that the functions act on the right.
May
26
comment Semigroup with exactly one left(right) identity?
@user4514: Ah, I should have specified which side the functions are acting on, as obviously it makes a difference. I'll fix this now.