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

location  New York City  
age  42  
visits  member for  3 years, 9 months 
seen  3 hours ago  
stats  profile views  7,802 
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/
2d

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Differences between primitive central idempotents and primitive orthogonal idempotents
Yes it is. ...... 
Mar 25 
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Number of trivializations of a trivial word in the free group
I suspect I misunderstood what you had wanted. I some how thought you wanted to count the number of trivializations of elements of length 2n rather than the number of elements of length 2n with exactly m trivializations. 
Mar 25 
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Differences between primitive central idempotents and primitive orthogonal idempotents
I think what the OP wants is that a complete set of orthogonal primitive idempotents for the center of A gives a decomposition of A into indecomposable twosided ideals (i.e. gives a decomposition of A into indecomposable AA bimodules). 
Mar 24 
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Uninteresting questions with interesting answers
My point is to disagree with the question being uninteresting. I think the question of which diophantine problems have solutions goes back to the earliest days of mathematics and is as natural as any mathematical problem I can imagine and I am not a number theorist. So I really don't think the problem was uninteresting until the answer was known. 
Mar 24 
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Uninteresting questions with interesting answers
I would say that the problem is interesting and natural. Hilbert almost surely thought there would be an algorithm and was undoubtedly aware that many natural algorithmic problems are naturally (as opposed to the Halting problem) diophantine problems. 
Mar 24 
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Which way for reading the proofs?
I flagged to make CW since there is clearly no one correct answer. 
Mar 23 
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Number of trivializations of a trivial word in the free group
I think Richard Stanley's enumerative combinatorics volume 2 has it. There is also the SedgwickFlajolet book on analytic combinatorics. A more technical book is Salomaa's book on formal power series in formal language theory (there is a coauthor but I forget who). 
Mar 23 
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What are the applications of operator algebras to other areas?
I would suspect that Gelfands duality between unital commutative C*algebras and compact Hausdorff spaces had some influence on the definition of an affine scheme. 
Mar 23 
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Number of trivializations of a trivial word in the free group
You should be able to write an ambiguous contextfree grammar for the type of trivialization you define and use the Chomsky Schutzenberger method to get an algebraic generating function 
Mar 22 
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Goldie's Theorem for Semigroups
I think John Fountain and his students put a lot of effort into proving as good a semigroup analogue of Goldie's theorem as possible. You might contact him. 
Mar 22 
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What are the applications of operator algebras to other areas?
Isn't the BostConnes system supposed to tell us about the RiemannZeta? 
Mar 19 
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What is the name for the subring of the Grothendieck ring of a bialgebra spanned by onedimensional representations?
I think you are thinking of the case where you have a tower of algebras like symmetric group algebras and you first tensor and then induce to get a product on the direct sum of Grothendieck groups. Here I have no subalgebra to induce from. 
Mar 18 
asked  What is the name for the subring of the Grothendieck ring of a bialgebra spanned by onedimensional representations? 
Mar 17 
awarded  Nice Answer 
Mar 17 
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What interesting things do automorphism groups of trees act on?
There is a measure preserving action on the space of ends with respect to product of uniform measures. This gives a unitary representation on Hilbert space 
Mar 16 
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About the second largest adjacency eigenvalue of Abelian Cayley graphs
You should probably add that the group is abelian in the body of the question and not just in the title. 
Mar 13 
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Brandt's definition of groupoids (1926)
Mark Lawson's inverse semigroup book also mentions the work of Brandt. Nowadays people value these things Brandt inverse semigroups. 
Mar 13 
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Brandt's definition of groupoids (1926)
Eilenberg and Mac Lane in any event thought the big contribution of their paper was introducing natural transformations as the name of their paper suggests. 
Mar 13 
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Brandt's definition of groupoids (1926)
Brandt's work is well known to everyone who works in semigroup theory and is discussed in the ~1967 book on semigroups by Clifford and Preston. It is not surprising that groupoids appears before categories since the fundamental groupoid has essentially been there since Poincaré 
Mar 10 
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Decision problem on triviality of intersection of two subgroups
Isn't this what my added statement says except that I didn't emphasize that one of the subgroups is fixed? 