bio  website  sci.ccny.cuny.edu/~benjamin 

location  New York City  
age  42  
visits  member for  3 years, 10 months 
seen  33 mins ago  
stats  profile views  7,941 
I am an algebraist interested in a broad range of areas. I've worked on semigroups, geometric group theory, algebraic combinatorics, representation theory, selfsimilar groups (aka automaton groups), profinite groups and random walks on semigroups and groups. I've been particularly interested in interactions between these areas and Computer Science and am fond of algorithmic questions. I've also dabbled with operator algebras associated to etale groupoids and inverse semigroups. Currently, I am interested in applications of finite semigroup theory to finite state Markov chains.
My blog is http://bensteinberg.wordpress.com/author/bsteinbg/
16h

accepted  A question of terminology regarding integer partitions 
Apr 24 
comment 
A question of terminology regarding integer partitions
It will take me a moment to digest this. Thanks for the answer. 
Apr 24 
comment 
Profinite Topology
Some people found J*G=JmG weird. Perhaps I want V closed under extension and W locally finite 
Apr 23 
asked  A question of terminology regarding integer partitions 
Apr 23 
comment 
Profinite Topology
Maybe it is not true but It's my feeling 
Apr 23 
comment 
How to prove that a projective module is not free?
Is A a finite dimensional algebra over a field or at least finitely generated over a field or over Z? 
Apr 22 
comment 
“Diagonalizing” an associative algebra
You need more than commutative and semisimple in the finite dimensional case: you need that the algebra splits over the ground field. If the ground field is not algebraically closed, you can get commutative semisimple algebras which are not diagonalized by just taking an finite extension. 
Apr 20 
revised 
ProG_p*G_q topology, profinite topology
edited tags 
Apr 20 
comment 
What is the mathematical structure called if we replace commutative group by commutative monoid in the definition of linear space?
These things really should be called modules over semirings. If you are over a ring, you will get a module anyway so it is clear that the "deficiency" (or semi) is in the ``ring'' not the module. 
Apr 20 
comment 
ProG_p*G_q topology, profinite topology
This is wide open 
Apr 16 
comment 
Sets of natural numbers such that sums of a bounded number of its elements form a semigroup
Regular subsets of N are the union of a finite set with an arithmetic progression. Can anything be said about other sets? 
Apr 14 
revised 
pseudovarieties and profinite group : do * and g() commute?
edited body 
Apr 14 
comment 
pseudovarieties and profinite group : do * and g() commute?
Here it should be mentioned that semidirect products of categories are defined via the Grothendieck construction 
Apr 14 
revised 
pseudovarieties and profinite group : do * and g() commute?
edited tags 
Apr 14 
revised 
pseudovarieties and profinite group : do * and g() commute?
Fixed link 
Apr 14 
comment 
pseudovarieties and profinite group : do * and g() commute?
@YCor, it is the pseudovariety of categories generated by the monoids in V viewed as oneobject categories. 
Apr 14 
answered  pseudovarieties and profinite group : do * and g() commute? 
Apr 13 
awarded  Necromancer 
Apr 13 
comment 
classifying pairs of idempotent matrices
If the characteristic is not 2, then A is an idempotent iff I2A is an involution. So you are essentially looking at the representation type of the infinite dihedral group. Quick googling of representation type infinite dihedral group gave me a chapter of a book by Benson giving all indecomposables from which you can deduce tame 
Apr 11 
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Groups acting on complexes
Usually people just remove the center instead of e. The 1Skeleton is called the commuting graph. Lots of people look at this 