BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Matthew Kennedy (University of Waterloo) DTSTART:20201002T213000Z DTEND:20201002T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/1 DESCRIPTION:Title: Operator algebras and group theory\nby Matthew Ken nedy (University of Waterloo) as part of University of Regina math & stats colloquium\n\n\nAbstract\nSince the work of von Neumann\, the theory of o perator algebras has been closely linked to the theory of groups. On the o ne hand\, operator algebras constructed from groups provide an important s ource of examples and insight. On the other hand\, many problems about gro ups are most naturally studied within an operator-algebraic framework. In this talk I will introduce these ideas and discuss recent developments rel ating the structure of a group to the structure of a corresponding operato r algebra.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Davis (University of Louisiana at Lafayette) DTSTART:20201023T213000Z DTEND:20201023T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/2 DESCRIPTION:Title: Lifting trivial actions from group cohomology to spect ra\, for profinite groups\nby Daniel Davis (University of Louisiana at Lafayette) as part of University of Regina math & stats colloquium\n\n\nA bstract\nLet $G$ be a topological group that is compact\, Hausdorff\, and totally disconnected (such a group is "profinite")\, and let $A$ be any ab elian group. Then $A$ can be regarded as a $G$-module by letting $G$ act t rivially on $A$\, and it is a known result that the continuous group cohom ology of $G$ with coefficients in $A$ can be obtained by taking a "union" of the ordinary group cohomology of certain finite quotient groups of $G$ with the same coefficients.\n\nIn this talk\, we consider what happens whe n $A$ is replaced by any spectrum (in the sense of homotopy theory)\, and group cohomology\, which in degree $0$ is just the fixed points of the gro up action\, is replaced with homotopy fixed points. We give some condition s that guarantee that in this new setting\, there is an analogue of the af orementioned "known result".\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Michael Brannan (Texas A&M University) DTSTART:20201030T213000Z DTEND:20201030T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/3 DESCRIPTION:Title: Quantum graphs and quantum Cuntz-Krieger algebras\ nby Michael Brannan (Texas A&M University) as part of University of Regina math & stats colloquium\n\n\nAbstract\nIn this talk I will give a light i ntroduction to the theory of quantum graphs. Quantum graphs are generaliza tions of directed graphs within the framework of non-commutative geometry\ , and they arise naturally in a surprising variety of areas including quan tum information theory\, representation theory\, and in the theory of non- local games. I will give an overview of some of these connections and also explain how one can generalize the well-known construction of Cuntz-Krieg er $C^*$-algebras associated to ordinary graphs to the setting of quantum graphs. Time permitting\, I will also explain how quantum symmetries of q uantum graphs can be used to shed some light on the structure of quantum C untz-Krieger algebras. (This is joint work with Kari Eifler\, Christian V oigt\, and Moritz Weber.)\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrei Volodin (University of Regina) DTSTART:20201127T213000Z DTEND:20201127T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/4 DESCRIPTION:Title: On the Golden Ratio\, Strong Law\, and First Passage P roblem\nby Andrei Volodin (University of Regina) as part of University of Regina math & stats colloquium\n\n\nAbstract\nFor a sequence of correl ated square integrable random variables $\\{X_n\, n\\geq 1\\}$\, condition s are provided for the strong law of large numbers\n\\[\n\\lim_{n\\to \\in fty} \\frac{S_{n}- ES_{n} }{ n }=0\n\\]\nalmost surely to hold\, where $\\ S_{n}=\\sum^n_{i=1}{X_{i}}$. The hypotheses stipulate that two series con verge\, the terms of which involve\, respectively\, both the Golden Ratio $\\varphi=\\frac{1 + \\sqrt{5}}{2}$ and bounds on Var $X_n$ (respectively\ , bounds on Cov $(X_n\, X_{n+m}))$. An application to first passage times is provided.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Anna Marie Bohmann (Vanderbilt University) DTSTART:20210122T213000Z DTEND:20210122T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/5 DESCRIPTION:Title: Detecting algebraic structures: K-theory and Lawvere t heories\nby Anna Marie Bohmann (Vanderbilt University) as part of Univ ersity of Regina math & stats colloquium\n\n\nAbstract\nIn the 1950s and 6 0s\, mathematicians began constructing the invariants of rings that are ca lled "$K$-theory." The $K$-theory of rings is hard to compute\, but it co ntains lots of interesting information about algebra\, number theory\, and topology. For example\, $K$-theory detects when rings are "the same" in the sense of having suitably equivalent categories of modules\, which is c alled Morita invariance. In this talk\, I will discuss the $K$-theory of rings as well as new work with Markus Szymik about the $K$-theory of a mor e general kind of algebraic structure\, called a Lawvere theory. In the l atter case\, we show that while the $K$-theory of Lawvere theories contain s lots of interesting information\, it fails to satisfy Morita invariance! \n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Jason Crann (Carleton University) DTSTART:20210129T213000Z DTEND:20210129T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/6 DESCRIPTION:Title: Amenable dynamical systems through Herz--Schur multipl iers\nby Jason Crann (Carleton University) as part of University of Re gina math & stats colloquium\n\n\nAbstract\nThe Herz--Schur multiplier man ifestation of amenability provides a fundamental link between abstract har monic analysis and operator algebras\, allowing for a fruitful exchange of ideas and tools between the two areas. A generalized theory of Herz--Schu r multipliers for dynamical systems has recently emerged through independe nt work of Bedos--Conti and McKee--Todorov--Turowska.\n\nIn this talk\, we generalize the aforementioned link by establishing Herz--Schur multiplier characterizations of amenable $W^*$- and $C^*$-dynamical systems over arb itrary locally compact groups. As byproducts of our results\, we (1) answe r a question of Anantharaman-Delaroche and obtain a Reiter type characteri zation of amenable $W^*$-dynamical systems\, and (2) show that a commutati ve $C^*$-dynamical system $(C_0(X)\,G\,\\alpha)$ is amenable if and only i f the action of $G$ on $X$ is topologically amenable. Combined with recent work of Buss--Echterhoff--Willett\, this latter result implies the equiva lence between topological amenability and measurewise amenabilty for $G$-s paces $X$ when both $G$ and $X$ are second countable. This is joint work w ith Alex Bearden.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Seyed Ahmad Mojallal (University of Regina) DTSTART:20210305T213000Z DTEND:20210305T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/7 DESCRIPTION:Title: Applications of the vertex-clique incidence matrix of a graph\nby Seyed Ahmad Mojallal (University of Regina) as part of Uni versity of Regina math & stats colloquium\n\n\nAbstract\nIn this talk\, we make use of an interaction between the theory of clique partitions of a g raph and graph spectra. We use the theory of clique partitions and introdu ce the notion of a vertex-clique incidence matrix of the graph. We give ne w lower bounds for the negative eigenvalues and negative inertia of a grap h. Moreover\, utilizing vertex-clique incidence matrices\, we generalize s everal notions such as the signless Laplacian matrix and a line graph of a graph as well as the incidence energy and the signless Laplacian energy o f the graph.\n\nApplying a similar type of incidence matrices obtained fro m the theory of clique covering\, we report on some recent research studyi ng the minimum number of distinct eigenvalues of a graph.\n\nThis is joint work with Shaun Fallat.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/7/ END:VEVENT BEGIN:VEVENT SUMMARY:David Sherman (University of Virginia) DTSTART:20210319T213000Z DTEND:20210319T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/8 DESCRIPTION:Title: Model theory for functional analysis\nby David She rman (University of Virginia) as part of University of Regina math & stats colloquium\n\n\nAbstract\nModel theory studies the interplay between math ematical structures and their logical properties. Some of its most beauti ful theorems involve a construction called an ultrapower. Many standard o bjects in functional analysis\, such as Banach spaces and operator algebra s\, carry useful notions of ultrapower\, but this does not interact well w ith classical model theory. An elegant solution\, very natural for analys ts\, is to switch to a logic in which truth values are drawn from the inte rval $[0\,1]$. I will give a "big picture" survey of this approach and it s prehistory\, not assuming that the audience has any familiarity with log ic or ultrapowers.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Ilijas Farah (York University) DTSTART:20210910T213000Z DTEND:20210910T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/9 DESCRIPTION:Title: Coarse geometry and rigidity\nby Ilijas Farah (Yor k University) as part of University of Regina math & stats colloquium\n\n\ nAbstract\nCoarse geometry is the study of metric spaces when one forgets about the small scale structure and focuses only on the large scale. For e xample\, this philosophy underlies much of geometric group theory. To a c oarse space one associates an algebra of operators on a Hilbert space\, ca lled the uniform Roe algebra. No familiarity with coarse geometry\, opera tor algebras\, or logic is required. After introducing the basics of coar se spaces and uniform Roe algebras\, we will consider the following rigidi ty questions:\n\n(1) If the uniform Roe algebras associated to coarse spac es X and Y are isomorphic\, when can we conclude that X and Y are coarsely equivalent?\n\n(2) The uniform Roe corona is obtained by modding out the compact operators. If the uniform Roe coronas of X and Y are isomorphic\, what can we conclude about the relation between the underlying uniform Roe algebras (or about the relation between X and Y)? \n\nThe answers to thes e questions are fairly surprising. This talk is based on a joint work with F. Baudier\, B.M. Braga\, A. Khukhro\, A. Vignati\, and R. Willett.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Maria Gillespie (Colorado State University) DTSTART:20211001T213000Z DTEND:20211001T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/10 DESCRIPTION:Title: Tournaments and the geometry of curves\nby Maria Gillespie (Colorado State University) as part of University of Regina math & stats colloquium\n\n\nAbstract\nHow many lines pass through four given fixed lines in three dimensional space? How many cubic curves in three di mensions pass through 5 given points and are also tangent to two fixed pla nes? \n\nThe first question is a classical problem of "Schubert calculus" \, and can be solved via a simple count of combinatorial objects called Yo ung tableaux. The second can be approached using intersection theory on m oduli spaces of curves\, and in this talk we present new combinatorial met hods via algorithms on labeled trees called "tournaments" that enable us t o more easily solve enumerative problems about curves. These results are due to joint work with Sean Griffin and Jake Levinson.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicholas Scoville (Ursinus College) DTSTART:20211203T213000Z DTEND:20211203T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/11 DESCRIPTION:Title: Towards a new digital homotopy theory\nby Nichola s Scoville (Ursinus College) as part of University of Regina math & stats colloquium\n\n\nAbstract\nWe present recent progress with collaborators Gr eg Lupton and John Oprea towards developing a digital version of homotopy theory. An $n$-dimensional digital image is a finite subset of the intege r lattice along with an adjacency relation. Although there are many paper s on digital homotopy theory\, many of the notions do not seem satisfacto ry from a homotopy point of view. Indeed\, some of the constructs most us eful in homotopy theory\, such as cofibrations and path spaces\, are absen t from the literature or completely trivial.\n\nWorking in the digital set ting\, we develop some basic ideas of homotopy theory\, including cofibrat ions and path fibrations\, in a way that seems more suited to homotopy the ory. We will indicate how our approach may be used\, for example\, to stu dy Lusternik-Schnirelmann category in a digital setting. One future goal is to develop a characterization of a "homotopy circle" (in the digital se tting) using the notion of topological complexity. This is with a view to wards recognizing circles\, and perhaps other features\, using these ideas . This talk will introduce some of the basics of digital topology and wil l not require any specialized background.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Jesse Peterson (Vanderbilt University) DTSTART:20220204T213000Z DTEND:20220204T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/12 DESCRIPTION:Title: Character Rigidity in Higher-Rank Groups\nby Jess e Peterson (Vanderbilt University) as part of University of Regina math & stats colloquium\n\n\nAbstract\nA character on a group is a class function of positive type. For finite groups\, the classification of characters is closely related to the representation theory of the group and plays a key role in the classification of finite simple groups. Based on the rigidity results of Mostow\, Margulis\, and Zimmer\, it was conjectured by Connes that for lattices in higher rank simple Lie groups\, the space of characte rs should be completely determined by their finite dimensional representat ions. In this talk\, I will discuss the solution to this conjecture\, as w ell as a recent remarkable extension by Boutonnet and Houdayer. I will als o discuss the relationship to ergodic theory\, invariant random subgroups\ , and von Neumann algebras.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Benjamin Steinberg (City College of New York) DTSTART:20220218T213000Z DTEND:20220218T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/13 DESCRIPTION:Title: Factoring the Dedekind-Frobenius determinant\nby Benjamin Steinberg (City College of New York) as part of University of Reg ina math & stats colloquium\n\n\nAbstract\nIn 1875\, Smith computed the de terminant of the $n \\times n$ matrix whose $(i\,j)$-entry is $\\gcd(i\,j) $. This matrix is nothing other than the multiplication table of the semig roup $\\{ 1\, \\ldots\, n \\}$ under the binary operation of gcd. Dedekind introduced in 1896\, in correspondence with Frobenius\, the group determi nant of a finite group\, which is the formal determinant of the multiplica tion table of the group. His motivation came from trying to compute the di scriminant of a finite Galois extension of $\\mathbb{Q}$. Frobenius famous ly invented the representation theory of finite groups precisely to factor Dedekind's group determinant. Studying a generalization of the group dete rminant also led Frobenius to characterizing the algebras nowadays called Frobenius algebras.\n\nOf course\, there is no reason to only compute the determinant of a group multiplication table. People have looked at both se migroups and Latin squares. Generalizing the work of Smith mentioned earli er\, Lindstrom and Wilf independently published papers in 1967 computing t he semigroup determinant of a meet semilattice. For Wilf\, the primary mot ivation was to compute determinants of various matrices arising from combi natorial objects and his paper\, entitled "Hadamard determinants\, Mobius functions\, and the chromatic number of a graph"\, was published in the Bu lletin of the AMS.\n\nIn 1998\, Jay Wood\, who works in Coding theory\, fa ctored the determinant of the multiplicative semigroup of a finite commuta tive chain ring\; these are rings whose ideals form a chain like $\\mathbb {Z}/p^n \\mathbb{Z}$ with $p$ a prime. His motivation was to prove a gener alization of the MacWilliams extension theorem for codes over a finite fie ld to codes over a finite ring. This theorem says that a partial isometry between codes can be extended to a global isometry with respect to the Ham ming metric. Eventually\, it was shown using methods unrelated to semigrou p determinants that the MacWilliams extension theorem holds precisely for finite Frobenius rings.\n\nIn this talk\, I'll survey some results I've ob tained in a more systematic attempt to factor the semigroup determinant. T he semigroup determinant is a special case of Frobenius's paratrophic dete rminant of an algebra and so the semigroup determinant is nonzero if and o nly if the semigroup algebra is Frobenius. Our main results are a factoriz ation of the determinant of an inverse semigroup (generalizing simultaneou sly Frobenius and the Lindstrom-Wilf theorem) and a factorization of the s emigroup determinant of a commutative semigroup. Our final result says tha t the semigroup algebra of a finite Frobenius ring is a Frobenius algebra. This implies as a special case the celebrated result of Okninski and Putc ha that every complex representation of the multiplicative semigroup of $n \\times n$ matrices over a finite field is completely reducible. It also suggests that the MacWilliams extension theorem for finite Frobenius rings should be provable using the semigroup determinant method.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Vesna Stojanoska (University of Illinois at Urbana-Champaign) DTSTART:20220318T213000Z DTEND:20220318T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/14 DESCRIPTION:Title: Duality for some Galois groups in stable homotopy the ory\nby Vesna Stojanoska (University of Illinois at Urbana-Champaign) as part of University of Regina math & stats colloquium\n\n\nAbstract\nIn classical algebra\, the integer primes $p$ help decompose objects as well as problems into their $p$-primary parts\, which may be easier to study. T he same is true in homotopy theory\, but the situation is more interesting since for each integer prime $p$\, there are infinitely many nested homot opical primes. For each of those homotopical primes\, there is an (unramif ied) Galois group that governs the local story and encodes the symmetries of chromatic homotopy theory. These Galois groups turn out to be particula rly nice profinite groups\, known as compact $p$-adic analytic. Such group s and their fascinating duality properties within algebra were studied by Lazard. I will try to explain a newer result\, which shows that their homo topical duality properties are even better\, giving powerful implications for the chromatic Galois extensions that they govern.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Ada Chan (York University) DTSTART:20220401T213000Z DTEND:20220401T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/15 DESCRIPTION:Title: State transfer in complex quantum walks\nby Ada C han (York University) as part of University of Regina math & stats colloqu ium\n\n\nAbstract\nThe continuous-time quantum walk on a finite graph $X$ is defined by the time-dependent unitary matrix \n\\[\nU(t) = e^{itH}\,\n\ \]\nwhere the Hamiltonian $H$ is some Hermitian matrix associated with $ X$. Perfect state transfer from vertex $a$ to vertex $b$ occurs if $U(t)_{ b\,a}$ has unit magnitude at some time $t$. This phenomenon is relevant fo r information transmission in quantum spin networks. Most previous studies on perfect state transfer used the adjacency matrix or the Laplacian mat rix of $X$ as the Hamiltonian. \n\nIn this talk\, we focus on continuous -time quantum walks with complex Hamiltonian. We examine how state transf er with complex Hamiltonian behaves differently from the quantum walks who se Hamiltonian is the adjacency matrix or the Laplacian matrix of a graph. \n\nThis is joint work with Chris Godsil\, Christino Tamon\, Xiaohong Zhan g\, and Fields undergraduate summer research students Antonio Acuaviva\, S ummer Elridge\, Matthew How and Emily Wright.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Ferdinand Ihringer (Ghent University) DTSTART:20220603T213000Z DTEND:20220603T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/16 DESCRIPTION:Title: Caps and Probabilistic Methods\nby Ferdinand Ihri nger (Ghent University) as part of University of Regina math & stats collo quium\n\nLecture held in RI 208 (Research and Innovation Centre).\n\nAbstr act\nA set of points in a finite projective space $\\mathrm{PG}(n\, q)$ wi th no three collinear is called a cap. More generally\, a set of po ints in $\\mathrm{PG}(n\, q)$ such that no $s$-space contains more than $r $ points is called an $(r\, s\; n\, q)$-set. In the first (and main) part of the talk we will discuss probabilisitic approaches to this classical pr oblem.\n\nIn the second part of the talk\, if time permits\, we will discu ss one reason why it is so hard to construct large caps. For this we prese nt parameter restrictions on approximately strongly regular graphs. This is joint work with Jacques Verstraëte.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Inna Zakharevich (Cornell University) DTSTART:20221007T213000Z DTEND:20221007T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/17 DESCRIPTION:Title: Point counting with twists\nby Inna Zakharevich ( Cornell University) as part of University of Regina math & stats colloquiu m\n\n\nAbstract\nConsider a variety over a finite field. The number of poi nts over the field is not only an invariant of the variety\, but also of i ts "scissors congruence" type: of we cut up the variety into locally close d pieces\, and rearrange those pieces into another variety\, the number of points does not change. Moreover\, if we have an automorphism of a variet y\, the permutation induced on the points is similarly an invariant of the automorphism. In this talk we will discuss a way of enhancing this invari ant to an invariant which can distinguish different types of automorphisms and use it to detect some interesting structures in the higher $K$-theory groups of varieties.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniel Soskin (University of Notre Dame) DTSTART:20230113T213000Z DTEND:20230113T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/18 DESCRIPTION:Title: Determinantal inequalities for totally positive matri ces\nby Daniel Soskin (University of Notre Dame) as part of University of Regina math & stats colloquium\n\n\nAbstract\nTotally positive matrice s are matrices in which each minor is positive. Lusztig extended the notio n to reductive Lie groups. He also proved that specialization of elements of the dual canonical basis in representation theory of quantum groups at $q=1$ are totally non-negative polynomials. Thus\, it is important to inve stigate classes of functions on matrices that are positive on totally posi tive matrices. I will discuss two sources of such functions. One has to do with multiplicative determinantal inequalities (joint work with M. Gekhtm an). Another deals with majorizing monotonicity of symmetrized Fischer's p roducts which are known for hermitian positive semidefinite case which bri ngs additional motivation to verify if they hold for totally positive matr ices as well (joint work with M. Skandera). The main tools we employed are network parametrization\, Temperley-Lieb and monomial trace immanants.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Colin Ingalls (Carleton University) DTSTART:20230317T213000Z DTEND:20230317T223000Z DTSTAMP:20260404T110832Z UID:ReginaMathColloquium/19 DESCRIPTION:Title: Groupoids (Stacks) associated with non-commutative su rfaces\nby Colin Ingalls (Carleton University) as part of University o f Regina math & stats colloquium\n\n\nAbstract\nThis is joint work with El eonore Faber\, Matthew Satriano\, and Shinnosuke Okawa. This will be a gen eral audience talk. One of the main constructions of Connes' noncommutativ e geometry is a construction of the convolution algebra of a groupoid. It is not clear how to characterize which algebras can be obtained this way. We construct a groupoid associated to a smooth\, finite over its centre\, noncommutative surface which has the same category of modules. This was do ne locally by Reiten and Van den bergh and in dimension one by Chan and I. We hope to use this result to study Artin's conjectured classification of noncommutative surfaces by reduction to characteristic $p$.\n LOCATION:https://stable.researchseminars.org/talk/ReginaMathColloquium/19/ END:VEVENT END:VCALENDAR