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The aim of the paper is to attach a noncommutative cluster-like structure to each marked surface $Sigma$. This is a noncommutative algebra ${mathcal A}_Sigma$ generated by noncommutative geodesics between marked points subject to certain triangle relations and noncommutative analogues of Ptolemy-Plucker relations. It turns out that the algebra ${mathcal A}_Sigma$ exhibits a noncommutative Laurent Phenomenon with respect to any triangulation of $Sigma$, which confirms its cluster nature. As a surprising byproduct, we obtain a new topological invariant of $Sigma$, which is a free or a 1-relator group easily computable in terms of any triangulation of $Sigma$. Another application is the proof of Laurentness and positivity of certain discrete noncommutative integrable systems.
The goal of this paper is to introduce and study noncommutative Catalan numbers $C_n$ which belong to the free Laurent polynomial algebra in $n$ generators. Our noncommutative numbers admit interesting (commutative and noncommutative) specializations, one of them related to Garsia-Haiman $(q,t
In this paper, we prove that a non-semisimple Hopf algebra H of dimension 4p with p an odd prime over an algebraically closed field of characteristic zero is pointed provided H contains more than two group-like elements. In particular, we prove that
In this paper we introduce a trace-like invariant for the irreducible representations of a finite dimensional complex Hopf algebra H. We do so by considering the trace of the map induced by the antipode S on the endomorphisms End(V) of a self-dual mo
We derive a formula for the trace of the antipode on endomorphism algebras of simple self-dual modules of nilpotent liftings of quantum planes. We show that the trace is equal to the quantum dimension of the module up to a nonzero scalar depending on the simple module.
We introduce a new filtration on Hopf algebras, the standard filtration, generalizing the coradical filtration. Its zeroth term, called the Hopf coradical, is the subalgebra generated by the coradical. We give a structure theorem: any Hopf algebra wi