From propp(at-sign)math.mit.edu Wed Sep 13 12:13:54 1995 To: combinatorics(at-sign)math.mit.edu Subject: MIT Combinatorics Seminar: September schedule MIT COMBINATORICS SEMINAR Here is a list of talks currently scheduled for the month of September. Notice that talks will normally begin at 4:35 p.m. If you have an interest in presenting something short (as in last semester's "combinatorial free-for-all"), let me know; if there's enough interest, I will organize another free-for-all later in the term. Wednesday, September 20, 4:35 p.m.: Joseph Bonin, Matroids with no (q+2)-point-line minors Friday, September 22, 4:35 p.m.: William Jockusch, Antisymmetric monotone triangles and domino tilings of quartered Aztec diamonds Friday, September 29, 4:35 p.m.: Karen Collins, Symmetry breaking in graphs From propp(at-sign)math.mit.edu Wed Sep 13 12:44:27 1995 To: combinatorics(at-sign)math.mit.edu Subject: Bonin, 9/20 Wednesday, September 20, 4:35 p.m.; MIT, room 2-338 Joseph Bonin (GWU and MIT) Matroids with no (q+2)-point-line minors We are concerned with U(q), the class of matroids containing no minor isomorphic to the (q+2)-point line. This class is of interest in part because of its connections with representability questions and its role in extremal matroid theory, in particular, in connection with size functions. For any prime power q, L(q) is a subset of U(q), where L(q) is the class of matroids representable over GF(q). In 1958, Tutte proved that L(2) = U(2). We will give a new proof of Tutte's theorem and sketch several other applications of the techniques used. For prime powers q>2, the (q+2)-point line is not the only excluded minor for GF(q)-representability. However, we show that with enough points in a geometry, the (q+2)-point line is the only minor one must exclude to guarantee that the geometry is representable over GF(q). Indeed, such geometries are uniquely representable over GF(q). We will apply these ideas to bound the size function of U(q) and to obtain a simple counting characterization of affine space. From propp(at-sign)math.mit.edu Fri Sep 15 08:36:37 1995 To: combinatorics(at-sign)math.mit.edu Subject: MIT Combinatorics Seminar (October slots) There are still some open slots for October; anyone wishing to speak on October 18 or 27 should contact me as soon as possible. (I will need a title and abstract by the beginning of next week.) Jim Propp From propp(at-sign)math.mit.edu Tue Sep 19 23:46:09 1995 To: combinatorics(at-sign)math.mit.edu Subject: Jockusch, 9/22 Friday, September 22, 4:35 p.m.; MIT, room 2-338 William Jockusch Antisymmetric monotone triangles and domino tilings of quartered Aztec diamonds In earlier work it was shown that the Aztec diamond of order n has 2^{n(n+1)/2} domino-tilings, and connections were established with monotone triangles and alternating sign matrices. In this talk I will describe follow-up work that establishes formulas for the number of domino-tilings of a ``quarter'' of an Aztec diamond of order n, with different formulas depending on exactly how the quartering is done as well as on the residue of n mod 4. This turns out to be a special case of a more general enumeration problem, where the number of domino-tilings of a certain kind of region is always equal to a power of 2 times the dimension of a particular representation of a Lie algebra. Our method of proof uses a weighted count of certain sorts of monotone triangles. Interestingly, if one considers other enumeration problems for these monotone triangles, one gets conjectural product-formulas that generalize earlier conjectures of Mills, Robbins and Rumsey. This is joint work with Jim Propp. From propp(at-sign)math.mit.edu Wed Sep 20 20:14:04 1995 To: combinatorics(at-sign)math.mit.edu Subject: Rota seminar Gian-Carlo Rota's seminar on invariant theory, combinatorics, and supersymmetric algebra will have its first meeting on Friday, Sept. 22 at 6 p.m. in 2-338. From propp(at-sign)math.mit.edu Fri Sep 22 12:10:00 1995 To: combinatorics(at-sign)math.mit.edu Subject: Collins, 9/29 Friday, September 29, 4:35 p.m.; MIT, room 2-338 Karen Collins (Wesleyan) Symmetry breaking in graphs A classic elementary problem with a surprise answer is the following: if a circular key ring holds n identically shaped keys, and in order to tell them apart, we plan to affix to each one a colored label, what is the minimum number of different colors needed to distinguish the keys? The surprise is that if n is at least 6, there need only be 2 different colors of labels; but if there are three, four, or five keys on the ring, there must be 3 different colors of labels. If we consider the keys as vertices in the n-cycle, then the effect of the labels on the vertices is to destroy every symmetry of the n-cycle. Define a labeling of a graph G, l:V(G) --> {1,2,...,r}, to be _r-distinguishing_ if no automorphism of G preserves all of the vertex labels. Then a natural question is, for any graph G, what is the minimum r such that G is r-distinguished? For an n-cycle, the answer is 3 if n=3,4,5 and 2 if n is at least 6. For a complete graph on m vertices, the answer is m. We give a bound on the minimum distinguishing number of a graph in terms of the order of its automorphism group, as well as finding the distinguishing numbers of graphs whose automorphism groups are abelian, dihedral, S_3, or S_4. This is joint work with Michael Albertson. From propp(at-sign)math.mit.edu Fri Sep 22 18:55:50 1995 To: combinatorics(at-sign)math.mit.edu Subject: MIT Combinatorics Seminar: October schedule MIT COMBINATORICS SEMINAR Here is a list of talks currently scheduled for the month of October. Notice that talks scheduled on *Wednesdays* will normally begin at 4:35 p.m., but that talks scheduled on Fridays will begin at *4:15*. Wednesday, October 11, 4:35 p.m.: Joseph Bonin, A survey of Dowling lattices Friday, October 13, 4:15 p.m.: Tal Kubo, Conway's recursive sequence Wednesday, October 18, 4:35 p.m.: Thomas Sundquist, Pfaffians and theta functions Friday, October 20, 4:15 p.m.: Ruth Haas, Decomposing graphs into trees Wednesday, October 25, 4:35 p.m.: Kenneth Fan, Matchings and canonical forms for symmetric tensors Friday, October 27, 4:15 p.m.: Greg Kuperberg, Alternating-sign matrices and the Yang-Baxter equation All talks will meet in room 2-338. From propp(at-sign)math.mit.edu Fri Sep 22 20:33:52 1995 To: combinatorics(at-sign)math.mit.edu Subject: AMS meeting at Northeastern Participants in the MIT combinatorics seminar may be interested in attending the special session on ``Representation Theory and Combinatorics'' that will be held at Northeastern University as part of the AMS regional meeting on October 7 and 8. This special session will meet on Saturday, October 7 from 8:30 to 10:50 a.m. and from 2:30 to 6:05 p.m., and on Sunday, October 8 from 9:00 to 10:50 a.m. and from 2:30 to 5:35 p.m. From propp(at-sign)math.mit.edu Fri Sep 22 20:44:10 1995 To: combinatorics(at-sign)math.mit.edu Subject: more about AMS meeting There will also be special sessions on Graph Theory: Saturday, October 7, 8:30 a.m. to 10:50 a.m. Saturday, October 7, 2:30 p.m. to 5:50 p.m. Sunday, October 8, 8:30 a.m. to 10:50 a.m. Sunday, October 8, 2:30 p.m. to 5:50 p.m. and Discrete Geometry Saturday, October 7, 8:30 a.m. to 10:50 a.m. Saturday, October 7, 2:30 p.m. to 5:20 p.m. Sunday, October 8, 8:30 a.m. to 10:50 a.m. (There may also be a Sunday afternoon session in Discrete Geometry, for all I know; I only have partial information.) From rstan(at-sign)math.mit.edu Fri Sep 22 20:54:48 1995 To: combinatorics(at-sign)math.mit.edu Subject: AMS meeting at Northeastern II Here is the tentative schedule of talks for the special session on "Representation Theory and Combinatorics." Saturday, October 7 8:30 am C. Kenneth Fan (Harvard University) 9:00 am Peter Magyar (University of Utrecht) 9:30 am Mark Shimozono (Massachusetts Institute of Technology) 10:00 am Francesco Brenti (University of Perugia) 10:30 am J. Matthew Douglass (University of North Texas) 2:30 pm Philip Hanlon (University of Michigan) 3:00 pm Daniel Rockmore (Dartmouth College) 3:30 pm David Grabiner (Hebrew University) 4:00 pm Curtis Greene (Haverford College) 4:45 pm John Stembridge (University of Michigan) 5:15 pm Robert Proctor (University of North Carolina) 5:45 pm Adriano Garsia (University of California at San Diego) Sunday, October 8 8:30 am Sheila Sundaram (University of Miami) 9:00 am Michelle Wachs (University of Miami) 9:30 am Victor Reiner (University of Minnesota) 10:00 am William Doran (California Institute of Technology) 10:30 am Mark Haiman (University of California at San Diego) 2:30 pm Alexander Kirillov, Jr. (Yale University) 3:00 pm Pavel Etingof (Yale University) 3:30 pm Bernard Leclerc (University of Paris VII) 4:15 pm Toshiki Nakashima (University of Osaka) 4:45 pm Yan Soibelman (Kansas State University) 5:15 pm Eugene Stern (University of California at Berkeley) From dynsys(at-sign)gibbs.oit.unc.edu Sat Sep 23 10:42:13 1995 Reply-To: bhasselb(at-sign)diamond.tufts.edu Originator: dynsys(at-sign)gibbs.oit.unc.edu Sender: dynsys(at-sign)gibbs.oit.unc.edu To: Multiple recipients of list <dynsys(at-sign)gibbs.oit.unc.edu> Subject: AMS meeting October 7-8 X-Listprocessor-Version: 6.0 -- ListProcessor by Anastasios Kotsikonas Announcement of Special Sessions American Mathematical Society Northeastern Section Meeting Northeastern University, Boston, October 7-8, 1995 This meeting has two sessions of interest to dynamicists and all interested colleagues are cordially invited to attend. SPECIAL SESSION ON ERGODIC THEORY Organizers: Stanley Eigen, Eigen(at-sign)Northeastern.edu, Northeastern University V.S. Prasad, PrasadV(at-sign)Woods.UML.edu, UMass Lowell (& Tufts) Current information about this session is available from the organizers. The schedule is as follows: Saturday Morning 8:30 - 8:50 Bruce Kitchens Dynamics of Markov groups 9:00 - 9:20 Roy Adler Topological conjugacy of endomorphisms of the 2-torus 9:30 - 9:50 Jane Hawkins Characterizing mildly mixing actions using ratio sets and orbit equivalence. 10:00 - 10:20 Aimee S.A. Johnson Loosely Bernoulli in $Z^d$ 10:30 - 10:50 Cesar Silva Relatively weak mixing and infinite skew product entropy Saturday Afternoon 3:30 - 3:50 Adam Fieldsteel Dyadic equivalence to actions of completely positive entropy 4:00 - 4:20 Janet Whalen Kammeyer Restricted Orbit Equivalence for Actions of Discrete Amenable Groups 4:30 - 4:50 Jonthan King Interrelations between determinism, zero-entropy and orbit separation 5:00 - 5:20 Andres del Junco Construction of simple measure-preserving maps with prescribed automorphism group 5:30 - 5:50 Nicholas S. Ormes Strong Orbit Realization for Minimal Homeomorphisms Sunday Morning 8:30 - 8:50 Robbie Robinson Finite type property and topoloogical dynamics for polyominoe tiling dynamical systems 9:00 - 9:30 Boris Solomyak Ergodic theory of non-periodic tilings. 9:30 - 9:50 Charles Radin Ergodic theory and the symmetry of tilings 10:00 - 10:20 James Propp A law of large numbers for the random domino tiling process Sunday Afternoon 2:30 - 2:50 Geoff Goodson $G$-Maps in the Centralizer of Compact Abelian Group Extensions. 3:00 - 3:20 B. S. Yadav The Mean-Ergodic Theorem and Spectral Decomposition of Complete isometries 3:30 - 3:50 Gary L. Raduns, Jr. Comparison of Generalizations of the Hopf Decomposition. SPECIAL SESSION ON GEOMETRIC AND HYPERBOLIC DYNAMICS Organizers: Zbigniew Nitecki, ZNitecki(at-sign)Tufts.edu, Tufts University Boris Hasselblatt, BHasselb(at-sign)Tufts.edu, Tufts University Current information about this session is available on the Worldwide Web under the URL http://www.tufts.edu/~bhasselb/amsmtg.html, and from the organizers. Saturday, October 7 9:30 Juan Tolosa (Stockton College of New Jersey) Pattern families 10:00 Marco Martens (SUNY Stony Brook) Hyperbolicity of Circle Renormalization 10:30 Mark Levi (Rensselaer Polytechnic Institute) Deterministic randomness with positive probability 2:40 Michael Shub (IBM) Stable Ergodicity and Partial Hyperbolicity (40 minutes) 3:30 Slobodan Simic (UC Berkeley) Synchronization of Anosov flows 4:00 Cymra Haskell (SUNY Stony Brook) The Infinite Periodic Lorentz Gas is Space-Time Bernoulli 4:30 Amie Wilkinson (UC Berkeley) Stable ergodicity of maps arising from geodesic flows 5:00 Fern Hunt (National Institute of Standards and Technology) Approximation of Attractors by Ulam's Method Sunday, October 8: 9:00 Ami Radunskaya KAM theory and the Fermi-Pasta-Ulam string model 9:30 Tasso Kaper (Boston University) Hyperbolicity in near-integrable N degrees-of-freedom Hamiltonian systems 10:00 Pau Atela (Smith College) A remarkable global bifurcation diagram in a Hamiltonian system 10:30 Dmitri Kleinbock (Yale University) Nondense orbits of flows on homogeneous spaces 2:30 Andrei Torok and Viorel Nitica (Princeton U. & Indiana U. Bloomington) Regularity of solutions for cocycle equations 3:00 Alexei Kononenko (Pennsylvania State University) Cohomologies of group actions and their applications 3:30 Nantian Qian (Yale University) Smooth conjugacy for Anosov diffeomorphisms and rigidity of Anosov actions of higher rank lattices 4:00 Henk Bruin (Universitat Erlangen) Cantor-attractors for interval maps Stan Eigen would like to invite all participants to the following event: Ig Nobel Award Ceremony October 6, 1995, 7:30 PM Lowell Hall, Harvard University (Tickets need to be bought in advance; contact info(at-sign)improb.com.) From kcollins(at-sign)MAIL.WESLEYAN.EDU Mon Sep 25 11:41:38 1995 X-Sender: kcollins(at-sign)mail.wesleyan.edu To: combinatorics(at-sign)math.mit.edu MIME-version: 1.0 Content-type: text/plain; charset="us-ascii" Content-transfer-encoding: 7BIT Here is the tentative schedule of talks for the special session on "Graph Theory." Saturday, Oct. 7, 1995 8:30 Nancy Eaton, Univ. of Rhode Island 9:00 C. Zhang, W. Virginia University 9:30 Ruth Haas, Smith College 10:00 Claude Tardif, University of Montreal 10:30 Gena Hahn, University of Montreal 2:30 Gara Pruesse, University of Vermont 3:00 Lenwood Heath, Virginia Polytech Inst. & State Univ. 3:30 Kathy McKeon, Conn. College 4:00 BREAK 4:30 Linda Lesniak, Drew University 5:00 Daniel Kleitman, MIT 5:30 Seth Chaiken, SUNY Albany Sunday, Oct. 8, 1995 8:30 Lauren Rose, Wellesley College 9:00 Brigitte Servatius, WPI 9:30 Herman Servatius, MIT 10:00 Karen Collins, Wesleyan Univ. 10:30 Michael Albertson, Smith College 2:30 Ann Trenk, Wellesley College 3:00 Ken Bogart, Dartmouth College 3:30 Ross McConnell, Amherst College 4:00 BREAK 4:30 Dave Berman, Univ. of New Orleans 5:00 Emily Petrie, Arizona State Univ. 5:30 Kathleen Romanik, DIMACS --------------------------- Department of Mathematics Wesleyan University Middletown CT 06459-0128 Fax: (860) 685-2571 --------------------------- From propp(at-sign)math.mit.edu Tue Oct 3 00:00:19 1995 To: combinatorics(at-sign)math.mit.edu Subject: Bonin, 10/11 Wednesday, October 11, 4:35 p.m.; MIT, room 2-338 Joseph Bonin (George Washington University and MIT): A survey of Dowling lattices Dowling lattices arose in connection with the theory of linear codes and as q-analogs of partition lattices, and they were quickly seen to be of use for studying arrangements of hyperplanes. These geometric lattices also provided the motivation for biased graphs, and, like projective spaces and free matroids, they are the universal models for one of the five types of varieties of combinatorial geometries. This talk will provide an introduction to these lattices and will outline several recent advances in the theory. The first class of results to be treated brings out similarities between Dowling lattices and projective spaces. This includes an axiom scheme for Dowling lattices, analogs of Desargues' and Pappus' theorems, and a coordinatization theory analogous to that for projective spaces. We will also present an application of the automorphism theory for Dowling lattices. The second collection of results to be discussed involves the Tutte polynomial, the matroid counterpart of the dichromatic polynomial of graph theory. The Tutte polynomial of any matroid contains much information about the matroid, and this is especially true for Dowling lattices. We will explore exactly how much information about a Dowling lattice is reflected in its Tutte polynomial. From propp(at-sign)math.mit.edu Tue Oct 3 00:00:24 1995 To: combinatorics(at-sign)math.mit.edu Subject: Kubo, 10/13 Friday, October 13, 4:15 p.m.; MIT, room 2-338 Tal Kubo (Harvard) Conway's recursive sequence Sequences obeying a(n) = a(a(n-1))+a(n-a(n-1)) have been explored by Conway, Hofstadter, Mallows, Kleitman and others. They have beautiful and intricate properties: combinatorial (symmetry, self-similarity), analytic (asymptotics related to the Gaussian distribution), and arithmetic (e.g., a(2^n)=2^{n-1}). We will show that a(n) can be viewed not as a complicated sequence, but as a simple compression operation on finite sets. Combinatorial structures including trees, Fibonacci and Catalan numbers, refinements of Pascal's triangle, and a mysterious appearance of Nim-like games, are encountered on the way. (These results were obtained in collaboration with R. Vakil.)

Date:Thu, 5 Oct 1995 12:08:12 -0400From:Jim Propp <propp(at-sign)math.mit.edu>To:tiling(at-sign)math.mit.eduSubject:Electronic Classroom

If latecomers to the UROP today find that 2-255 is empty, come look for us in 14-0637. (It's in the basement of the building that contains the Science Library.) Jim

Date:Fri, 6 Oct 1995 10:21:36 -0400 (EDT)From:Satomi Okazaki <satomi(at-sign)math.mit.edu>To:noetherian(at-sign)schauder.mit.edu, combinatorics(at-sign)schauder.mit.eduSubject:Reminder - Today at 5pm - Noetherian Ring seminar

The NOETHERIAN RING at MIT would like to announce biweekly half-hour talks given by women in mathematics followed by a half-hour for socializing and refreshments. The talks are meant to be accessible to a general mathematical audience. Everyone is welcome. Friday, October 6 5:00pm in room 2-136, MIT (please note room change) Professor Lynne M. Butler, Haverford College "An example of the topological perspective in combinatorics" Many beautiful theorems in algebraic topology have analogues in the theory of partially ordered sets. For example, Stanley discovered an Alexander duality theorem for Eulerian posets. In this talk we show how an observation of Matveev's, on how to compute the M\"obius number of a poset from edge coverings of its incomparability graph, may be quickly deduced from Stanley's Alexander duality theorem.

Date:Tue, 10 Oct 1995 18:09:27 -0400From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Sundquist, 10/18

Wednesday, October 18, 4:35 p.m.; MIT, room 2-338 Thomas Sundquist (Dartmouth) Pfaffians and theta functions The classical theory of Elliptic Functions gives rise to many interesting theta function identities such as P(b+e) P(b-e) P(c+d) P(c-d) - P(b+d) P(b-d) P(c+e) P(c-e) + q^(c-d) P(b+c) P(b-c) P(d+e) P(d-e) = 0, where P is a rescaled version of Jacobi's third theta function. The proofs of these identities typically are analytic, or rely on invoking standard facts about the finite dimensional space of modular forms of a given weight. Other theta function identities, like Jacobi's Triple Product which factors a theta function into three infinite products, have nice combinatorial interpretations and proofs. In this talk I will discuss a simple ``symmetric function theory'' proof of a generalization of the former identity. The technique involves expressing the combination of theta functions as the Pfaffian of a 4 by 4 skew-symmetric matrix, and then expanding the Pfaffian as a (vanishing) sum of alternants. Finally, we generalize the proof to give interesting expansions for Pfaffians of other ``theta-like'' functions.

Date:Tue, 10 Oct 1995 18:16:00 -0400From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Haas, 10/20

Friday, October 20, 4:15 p.m.; MIT, room 2-338 Ruth Haas (Smith) Decomposing graphs into trees The original characterization for when a graph can be decomposed into k spanning forests was given by Nash-Williams in 1964. In this talk we give several old and new characterizations for the following two classes of graphs: (i) graphs for which adding _some_ m edges produces a graph which is decomposable into k spanning trees, i.e., the graph has arboricity k; and (ii) graphs for which adding _any_ m edges produces a graph which is decomposable into k spanning trees. The study of the second of these is motivated by some results in combinatorial rigidity. In particular, a graph is rigid in the plane if it can be "constructed" using rigid bars for the edges and rotatable joints for the vertices so that the only possible motions in the plane are translation and rotation. Lovasz and Yemini showed that a graph is minimally rigid in the plane (removal of any edge would make it not rigid) if and only if adding any edge to the graph, including a multiple edge results in a graph which is decomposable into 2 spanning trees. A recent paper of Crapo gives another characterization of this class and it is this characterization that we extend to other cases.

Date:Wed, 11 Oct 1995 18:18:50 -0400From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Discrete Dinner

It's getting to be time to plan this semester's DISCRETE DINNER. If you have suggestions for a restaurant, please pass them on to me. Meanwhile, I'd like people's comments on the following dates: Wednesday, Nov. 1 Friday, Nov. 3 Wednesday, Nov. 8 Friday, Nov. 10 Wednesday, Nov. 15 Wednesday, Nov. 17 Jim

From:RHAAS(at-sign)smith.smith.eduDate:Sun, 15 Oct 1995 11:32:34 -0500 (EST)Subject:November 11th meeting of the Combinatorists of New EnglandTo:ramesh(at-sign)oahu.cs.umass.edu, aab(at-sign)christa.unh.edu, elcox(at-sign)conncoll.edu, epetrie(at-sign)emo.merrimack.edu, carducci(at-sign)lafvax.lafayette.edu, pak(at-sign)abel.math.harvard.edu, fomin%(at-sign)math.mit.edu, sara(at-sign)math.mit.edu, cathan(at-sign)math.mit.edu, apost(at-sign)math.mit.edu, lpachter(at-sign)math.mit.edu, dfinberg(at-sign)math.mit.edu, bona(at-sign)math.mit.edu, djk(at-sign)math.mit.edu, ariki(at-sign)math.mit.edu, mshimo(at-sign)math.mit.edu, satomi(at-sign)math.mit.edu, beveridg(at-sign)pascal.math.yale.edu, btesar(at-sign)mail.cog.jhu.edu, mloebl(at-sign)jeeves.uwaterloo.ca, JBONIN(at-sign)gwuvm.gwu.edu, rejam(at-sign)clemson.edu, peterrc(at-sign)wpi.edu, jziu(at-sign)maristb.marist.edu, lawsonn(at-sign)cs.rpi.edu, mathman(at-sign)brick.purchase.edu, ftbbb(at-sign)cunyvm.edu, spaletaj(at-sign)wpi.wpi.edu, atkins(at-sign)wpi.edu, elkies(at-sign)abel.math.harvard.edu, emann(at-sign)fas.harvard.edu, nate(at-sign)research.att.com, moorthy(at-sign)cs.rpi.edu, streinu(at-sign)grendel.csc.smith.edu, chung(at-sign)math.upenn.edu, jalfano(at-sign)eve.assumption.edu, bkitchens(at-sign)wesleyan.edu, hochberg(at-sign)math.rutgers.edu, jah(at-sign)christa.unh.edu, romanik(at-sign)dimacs.rutgers.edu, lenhart(at-sign)cs.williams.edu, sheila(at-sign)paris-gw.cs.miami.edu, pavol(at-sign)cs.sfu.ca, wantland(at-sign)mcs1.wcsu.ctstateu.edu, ross(at-sign)cs.amherst.edu, kia(at-sign)oregano.unh.edu, simion(at-sign)gwuvm.bitnet, innes(at-sign)cs.uri.edu, mcrystal(at-sign)bbn.com, finizio(at-sign)uriacc.uri.edu, macula(at-sign)geneseo.bitnet, kcirino(at-sign)lynx.dac.neu.edu, propp(at-sign)math.mit.edu, rstan(at-sign)math.mit.edu, combinatorics(at-sign)math.mit.edu, k.p.bogart(at-sign)dartmouth.edu, sdc(at-sign)cs.albany.edu, peterrc(at-sign)wpi.wpi.edu, kcollins(at-sign)eagle.wesleyan.edu, rhaas(at-sign)smith.smith.edu, lrose(at-sign)sallie.WELLESLEY.EDU, jjr(at-sign)linus.mitre.org, sandifer(at-sign)wcsub.ctstateu.edu, orourke(at-sign)sophia.smith.edu, senechal(at-sign)minkowski.smith.edu, immerman(at-sign)freya.cs.umass.edu, ccm(at-sign)cs.amherst.edu, diwan(at-sign)freya.cs.umass.edu, girkar(at-sign)freya.cs.umass.edu, grupen(at-sign)freya.cs.umass.edu, guruvado(at-sign)cs.umass.edu, herbordt(at-sign)cs.umass.edu, krithi%nirvan(at-sign)cs.umass.edu, lam(at-sign)cs.amherst.edu, liu(at-sign)freya.cs.umass.edu, lory(at-sign)freya.cs.umass.edu, atrenk(at-sign)sallie.WELLESLEY.EDU, landau(at-sign)freya.cs.umass.edu, malitz%oahu(at-sign)cs.umass.edu, rsnbrg(at-sign)freya.cs.umass.edu, adean(at-sign)skidmore.edu, jzca(at-sign)marist.bitnet, FRANZBLA(at-sign)dimacs.rutgers.edu, jhs(at-sign)math.cornell.edu, kamck(at-sign)mvax.cc.conncoll.edu, albertson(at-sign)smith.smith.edu, llangley(at-sign)carbon.denver.colorado.edu, Tom.Sundquist(at-sign)dartmouth.edu, rajpal(at-sign)griggs.dartmouth.edu, dbeers(at-sign)vmsvax.simmons.edu, bennett(at-sign)math.umass.edu, fishel(at-sign)scsud.ctstateu.edu, lenore(at-sign)math.mit.edu, gptesler(at-sign)euclid.ucsd.edu, streinu(at-sign)sophia.smith.edu, eaton(at-sign)cs.uri.edu, susan(at-sign)max.math.brandeis.edu, archdeac(at-sign)uvm-gen.emba.uvm.edu, kenney(at-sign)siena.bitnet, hutchinson(at-sign)macalstr.edu, lovasz-laszlo(at-sign)cs.yale.edu, plock(at-sign)stlawu.bitnet, dvella(at-sign)skidmore.edu, kwong(at-sign)mary.cs.fredonia.edu, lbutler(at-sign)acc.haverford.edu, jsims(at-sign)eagle.wesleyan.edu, ecoven(at-sign)eagle.wesleyan.edu, jlewis(at-sign)uriacc.uri.edu, sanjoy(at-sign)emba.uvm.edu, rjyanco(at-sign)unix.amherst.edu, gara(at-sign)emba.uvm.edu, ravi(at-sign)cs.uri.edu, quintas(at-sign)pacevm.dac.pace.edu, kennedyf(at-sign)pacevm.dac.pace.edu, lfeng(at-sign)eagle.wesleyan.edu, ssilberger(at-sign)eagle.wesleyan.edu, bheiles(at-sign)eagle.wesleyan.edu, krg(at-sign)rover.wellesley.edu, Rhoades(at-sign)emmy.smith.edu, hull(at-sign)cs.uri.edu, rajpal(at-sign)dartmouth.edu, silbergd(at-sign)snynewvm.bitnet

Come to the seventeenth one day conference on Combinatorics and Graph Theory Saturday, November 11, 1995 10 a.m. to 4:30 p.m. at Smith College Northampton MA 01063 Schedule 10:00 Esther Tesar (Drew University) Some Extensions of the Genus Distribution of Closed-End Ladders 11:10 Laszlo Lovasz (Yale University) The Matching Structure of Graphs 12:10 Lunch 2:00 Joe Bonin (George Washington University) A Survey of Dowling Lattices 3:10 Robert Jamison (Clemson University) Monotaxis in Matroids and Antimatroids Our Web page site has directions to Smith College, abstracts of speakers, dates of future conferences, and other information. The address is: http://math.smith.edu/~rhaas/coneweb.html We have received an NSF grant to support these conferences. This will allow us to provide a modest transportation allowance to those attendees who are not local. Michael Albertson (Smith College), (413) 585-3865, albertson(at-sign)smith.smith.edu Karen Collins (Wesleyan Univ.), (203) 685-2169, kcollins(at-sign)wesleyan.edu Ruth Haas (Smith College), (413) 585-3872, rhaas(at-sign)smith.smith.edu

Date:Wed, 18 Oct 1995 14:04:29 -0400From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Web-access for past postings

A self-updating archive of postings to the combinatorics mailing list (combinatorics(at-sign)math.mit.edu) during the last several years is now available on the Web: http://www-math.mit.edu/~propp/combinatorics_archive/ (The old archive on theory.lcs.mit.edu has been discontinued.) Jim Propp From propp(at-sign)math.mit.edu Wed Oct 18 15:41:04 1995 To: combinatorics(at-sign)math.mit.edu Subject: Fan, 10/25 Wednesday, October 25, 4:15 p.m.; MIT, room 2-338 C. Kenneth Fan (MIT): Matchings and canonical forms for symmetric tensors Let V be a q-dimensional vector space. Fix a set B of q(q-1) monomials in S^p(V) of the form x^I where i_k>0 for all k. The generic element of S^p(V) is conjugate under a suitable linear transformation to an element with support off of B. We prove this by showing the existence of a perfect matching with a unique weight in a certain weighted bipartite graph. Such a perfect matching corresponds to the non-vanishing of an appropriate determinant. This is joint work with Jozsef Losonczy. From propp(at-sign)math.mit.edu Wed Oct 18 15:47:15 1995 To: combinatorics(at-sign)math.mit.edu Subject: Kuperberg, 10/27 Friday, October 27, 4:15 p.m.; MIT, room 2-338 Greg Kuperberg (Yale) Alternating-sign matrices and the Yang-Baxter equation Robbins conjectured, and Zeilberger recently proved, that there are 1!4!7!...(3n-2)! ------------------ n!(n+1)!...(2n-1)! alternating sign matrices of order n. We will discuss a new proof of this result using an analysis of the six-vertex state model (also called square ice) based on the Yang-Baxter equation.

Date:Tue, 24 Oct 1995 15:16:05 -0400 (EDT)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Stanley, 11/3

Friday, November 3, 4:15 p.m.; MIT, room 2-338 Richard Stanley (MIT) Hyperplane arrangements, interval orders, and trees Abstract: A (real) hyperplane arrangement is a finite set of affine hyperplanes in R^n. A central problem in the theory of hyperplane arrangements is to count the number of regions into which the hyperplanes subdivide R^n. For instance, the number of regions of the arrangement (known as the _braid_arrangement_) consisting of all hyperplanes x_i = x_j, i<j, is easily seen to be n!. We will consider some modifications (deformations) of the braid arrangement and show some surprising connections with such topics as interval orders and the enumeration of trees. In particular, there is an explicit conjecture for the number of regions of the arrangement x_i - x_j=1, i<j. Much of this work was done in collaboration with Nati Linial, Igor Pak, Alexander Postnikov, and Schmulik Ravid.

Date:Tue, 24 Oct 1995 15:18:04 -0400 (EDT)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:DISCRETE DINNER

Fall 1995 Boston Area Discrete Mathematics Dinner This semester's Discrete Dinner will be held on Friday, November 3 at 6 p.m. at Thai's Restaurant (1 Kendall Square), just a few blocks from MIT. The cost will be $7 for grad students and undergraduates (not counting alcoholic beverages), with the rest of us making up the difference. I hope that the closeness to campus and the low cost of the meal will encourage graduate students and undergraduates to attend. Please let me know by October 31 (preferably electronically) your probability of attendance. My e-mail address is propp(at-sign)math.mit.edu; if you don't have e-mail, call 253-6544.

Date:Wed, 1 Nov 1995 15:36:59 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:MIT Combinatorics Seminar: November schedule

MIT COMBINATORICS SEMINAR Here is a list of talks currently scheduled for the month of November. Notice that talks scheduled on *Wednesdays* will begin at *4:35* p.m., but that talks scheduled on *Fridays* will begin at *4:15*. Friday, November 3, 4:15 p.m.: Richard Stanley, Hyperplane arrangements, interval orders, and trees (followed by Discrete Dinner) Wednesday, November 8, 4:35 p.m.: Ira Gessel, Counting binary trees by ascents and descents Wednesday, November 15, 4:35 p.m.: Miklos Bona, Permutations avoiding certain patterns Friday, November 17, 4:15 p.m.: David Jackson, The genus series for monopoles and the Euler characteristic for the moduli spaces of real algebraic curves Wednesday, November 29, 4:35 p.m.: Open mike (featuring Gian-Carlo Rota, Dan Kleitman, Christos Athanasiadis, and others) All talks will meet in room 2-338.

Date:Wed, 1 Nov 1995 15:37:39 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Gessel, 11/8

Wednesday, November 8, 4:35 p.m.; MIT, room 2-338 Ira Gessel (Brandeis) Counting binary trees by ascents and descents The number of unlabeled binary trees on n vertices is the Catalan number C_n={1 \over n+1}{2n \choose n}, so the number of labeled binary trees is n! C_n. We call a vertex of a labeled binary tree (with totally ordered vertices) a _left_ascent_ if it is a left child and is greater than its parent, and we define right ascents and left and right descents similarly. In this talk I will count labeled binary trees by left and right ascents and descents. Special cases yield Eulerian numbers and the number (n+1)^{n-1} of labeled rooted forests. There are also some non-obvious symmetries: There is a symmetry that switches left ascents with right descents, and by allowing repeated labels we obtain symmetric functions which I conjecture to be Schur-positive.

From:RHAAS(at-sign)smith.smith.eduDate:Wed, 08 Nov 1995 12:24:44 -0500 (EST)Subject:Schedule change for Saturday Nov 11 CONE meetingTo:lvsnyder(at-sign)amherst.edu, zamfi(at-sign)roz.hunter.cuny.edu, bservat(at-sign)wpi.wpi.edu, David.Mauro(at-sign)mail.cc.trincoll.edu, melanie.stein(at-sign)mail.cc.trincoll.edu, chen(at-sign)math.umass.edu, ramesh(at-sign)oahu.cs.umass.edu, aab(at-sign)christa.unh.edu, elcox(at-sign)conncoll.edu, epetrie(at-sign)emo.merrimack.edu, carducci(at-sign)lafvax.lafayette.edu, pak(at-sign)abel.math.harvard.edu, fomin%(at-sign)math.mit.edu, sara(at-sign)math.mit.edu, cathan(at-sign)math.mit.edu, apost(at-sign)math.mit.edu, lpachter(at-sign)math.mit.edu, dfinberg(at-sign)math.mit.edu, bona(at-sign)math.mit.edu, djk(at-sign)math.mit.edu, ariki(at-sign)math.mit.edu, mshimo(at-sign)math.mit.edu, satomi(at-sign)math.mit.edu, beveridg(at-sign)pascal.math.yale.edu, btesar(at-sign)mail.cog.jhu.edu, mloebl(at-sign)jeeves.uwaterloo.ca, JBONIN(at-sign)gwuvm.gwu.edu, rejam(at-sign)clemson.edu, peterrc(at-sign)wpi.edu, jziu(at-sign)maristb.marist.edu, lawsonn(at-sign)cs.rpi.edu, mathman(at-sign)brick.purchase.edu, ftbbb(at-sign)cunyvm.edu, spaletaj(at-sign)wpi.wpi.edu, elkies(at-sign)abel.math.harvard.edu, emann(at-sign)fas.harvard.edu, nate(at-sign)research.att.com, moorthy(at-sign)cs.rpi.edu, streinu(at-sign)grendel.csc.smith.edu, chung(at-sign)math.upenn.edu, jalfano(at-sign)eve.assumption.edu, bkitchens(at-sign)wesleyan.edu, hochberg(at-sign)math.rutgers.edu, jah(at-sign)christa.unh.edu, romanik(at-sign)dimacs.rutgers.edu, lenhart(at-sign)cs.williams.edu, sheila(at-sign)paris-gw.cs.miami.edu, pavol(at-sign)cs.sfu.ca, wantland(at-sign)mcs1.wcsu.ctstateu.edu, ross(at-sign)cs.amherst.edu, kia(at-sign)oregano.unh.edu, simion(at-sign)gwuvm.bitnet, innes(at-sign)cs.uri.edu, mcrystal(at-sign)bbn.com, finizio(at-sign)uriacc.uri.edu, macula(at-sign)geneseo.bitnet, kcirino(at-sign)lynx.dac.neu.edu, propp(at-sign)math.mit.edu, rstan(at-sign)math.mit.edu, combinatorics(at-sign)math.mit.edu, k.p.bogart(at-sign)dartmouth.edu, sdc(at-sign)cs.albany.edu, peterrc(at-sign)wpi.wpi.edu, kcollins(at-sign)eagle.wesleyan.edu, rhaas(at-sign)smith.smith.edu, lrose(at-sign)sallie.WELLESLEY.EDU, jjr(at-sign)linus.mitre.org, sandifer(at-sign)wcsub.ctstateu.edu, orourke(at-sign)sophia.smith.edu, senechal(at-sign)minkowski.smith.edu, immerman(at-sign)freya.cs.umass.edu, ccm(at-sign)cs.amherst.edu, diwan(at-sign)freya.cs.umass.edu, girkar(at-sign)freya.cs.umass.edu, grupen(at-sign)freya.cs.umass.edu, guruvado(at-sign)cs.umass.edu, herbordt(at-sign)cs.umass.edu, krithi%nirvan(at-sign)cs.umass.edu, lam(at-sign)cs.amherst.edu, liu(at-sign)freya.cs.umass.edu, lory(at-sign)freya.cs.umass.edu, atrenk(at-sign)sallie.WELLESLEY.EDU, landau(at-sign)freya.cs.umass.edu, malitz%oahu(at-sign)cs.umass.edu, rsnbrg(at-sign)freya.cs.umass.edu, adean(at-sign)skidmore.edu, jzca(at-sign)marist.bitnet, FRANZBLA(at-sign)dimacs.rutgers.edu, jhs(at-sign)math.cornell.edu, kamck(at-sign)mvax.cc.conncoll.edu, albertson(at-sign)smith.smith.edu, llangley(at-sign)carbon.denver.colorado.edu, Tom.Sundquist(at-sign)dartmouth.edu, rajpal(at-sign)griggs.dartmouth.edu, dbeers(at-sign)vmsvax.simmons.edu, bennett(at-sign)math.umass.edu, fishel(at-sign)scsud.ctstateu.edu, gptesler(at-sign)euclid.ucsd.edu, streinu(at-sign)sophia.smith.edu, eaton(at-sign)cs.uri.edu, susan(at-sign)max.math.brandeis.edu, archdeac(at-sign)uvm-gen.emba.uvm.edu, kenney(at-sign)siena.bitnet, hutchinson(at-sign)macalstr.edu, lovasz-laszlo(at-sign)cs.yale.edu, plock(at-sign)stlawu.bitnet, dvella(at-sign)skidmore.edu, kwong(at-sign)mary.cs.fredonia.edu, lbutler(at-sign)acc.haverford.edu, jsims(at-sign)eagle.wesleyan.edu, ecoven(at-sign)eagle.wesleyan.edu, jlewis(at-sign)uriacc.uri.edu, sanjoy(at-sign)emba.uvm.edu, rjyanco(at-sign)unix.amherst.edu, gara(at-sign)emba.uvm.edu, ravi(at-sign)cs.uri.edu, quintas(at-sign)pacevm.dac.pace.edu, kennedyf(at-sign)pacevm.dac.pace.edu, lfeng(at-sign)eagle.wesleyan.edu, ssilberger(at-sign)eagle.wesleyan.edu, bheiles(at-sign)eagle.wesleyan.edu, krg(at-sign)rover.wellesley.edu, Rhoades(at-sign)emmy.smith.edu, hull(at-sign)cs.uri.edu, rajpal(at-sign)dartmouth.edu, silbergd(at-sign)snynewvm.bitnet

REVISED SCHEDULE FOR: the seventeenth one day conference on Combinatorics and Graph Theory Saturday, November 11, 1995 10 a.m. to 4:30 p.m. at Smith College Northampton MA 01063 Schedule 10:00 Esther Tesar (Drew University) Some Extensions of the Genus Distribution of Closed-End Ladders 11:10 Laszlo Lovasz (Yale University) The Matching Structure of Graphs 12:10 Lunch 2:00 Joe Bonin (George Washington University) A Survey of Dowling Lattices 3:10 NEW TALK:: Ileana Streinu (Smith College) Visibility in Pseudo-Polygons and Vertex-Edge Pseudo-Visibility Graphs Our Web page site has directions to Smith College, abstracts of speakers, dates of future conferences, and other information. The address is: http://math.smith.edu/~rhaas/coneweb.html We have received an NSF grant to support these conferences. This will allow us to provide a modest transportation allowance to those attendees who are not local. Michael Albertson (Smith College), (413) 585-3865, albertson(at-sign)smith.smith.edu Karen Collins (Wesleyan Univ.), (203) 685-2169, kcollins(at-sign)wesleyan.edu Ruth Haas (Smith College), (413) 585-3872, rhaas(at-sign)smith.smith.edu

Date:Wed, 8 Nov 1995 16:29:41 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Bona, 11/15

Wednesday, November 15, 4:35 p.m.; MIT, room 2-338 Miklos Bona (MIT) Permutations avoiding certain patterns It is a long-studied, hard problem to determine how many permutations in S_n avoid a certain pattern q. The general conjecture claims that less than K^n, where K is a constant. Efforts to prove this have been unsuccessful for most patterns. (For two permutations a and b, it is NP-complete to decide whether a is a pattern of b; the problem of counting permutations in S_n avoiding q is #P-complete. Thus in general all we can expect is an upper bound or an asymptotical formula, not an exact formula). The only important cases in which the conjecture is known to be true were when k = 3 or when the pattern is monotonic. We improve these results showing that the_conjecture_on_the_exponential_ upper_bound_is_true_for_all_patterns_of_length_4. A conjecture states that if S_n(q_1) < S_n(q_2) for some n, then this inequality holds for all N > n. We prove this conjecture for patterns of length 4. These are the first results proving that one pattern is more likely to occur in a random permutation than another one. (Even in the asymptotical sense). Finally, we prove a lemma which allows us to extend our results to some longer patterns.

Date:Wed, 8 Nov 1995 19:22:01 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Jackson, 11/17

Friday, November 17, 4:15 p.m.; MIT, room 2-338 David Jackson (Waterloo) The genus series for monopoles and the Euler characteristic for the moduli spaces of real algebraic curves This question was solved for the complex case in 1986 by Harer and Zagier. A later argument was given by Penner. The real case, however, has remained open. In this talk I will give two arguments, that are combinatorial ones, which appeal 2-cell embeddings of graphs. The first argument is based on determining the genus series for monopoles (these are maps with one vertex) in locally orientable surfaces. This is of interest in its own right. The moduli space question can be expressed as a particular monopole problem (joint work with Goulden and Harer). This second problem can be treated by a classical theorem about multivariate integrals, to give a very simple explicit expression for the Euler characteristic. The integral representation for the case of orientable surfaces can also be given, and this gives a proof of the original result of Harer and Zagier that is direct.

From:eaton(at-sign)cs.uri.eduDate:Thu, 9 Nov 1995 10:05:41 +0100To:lvsnyder(at-sign)amherst.edu, zamfi(at-sign)roz.hunter.cuny.edu, bservat(at-sign)wpi.wpi.edu, David.Mauro(at-sign)mail.cc.trincoll.edu, melanie.stein(at-sign)mail.cc.trincoll.edu, chen(at-sign)math.umass.edu, ramesh(at-sign)oahu.cs.umass.edu, aab(at-sign)christa.unh.edu, elcox(at-sign)conncoll.edu, epetrie(at-sign)emo.merrimack.edu, carducci(at-sign)lafvax.lafayette.edu, pak(at-sign)abel.math.harvard.edu, fomin%(at-sign)math.mit.edu, sara(at-sign)math.mit.edu, cathan(at-sign)math.mit.edu, apost(at-sign)math.mit.edu, lpachter(at-sign)math.mit.edu, dfinberg(at-sign)math.mit.edu, bona(at-sign)math.mit.edu, djk(at-sign)math.mit.edu, ariki(at-sign)math.mit.edu, mshimo(at-sign)math.mit.edu, satomi(at-sign)math.mit.edu, beveridg(at-sign)pascal.math.yale.edu, btesar(at-sign)mail.cog.jhu.edu, mloebl(at-sign)jeeves.uwaterloo.ca, JBONIN(at-sign)gwuvm.gwu.edu, rejam(at-sign)clemson.edu, peterrc(at-sign)wpi.edu, jziu(at-sign)maristb.marist.edu, lawsonn(at-sign)cs.rpi.edu, mathman(at-sign)brick.purchase.edu, ftbbb(at-sign)cunyvm.edu, spaletaj(at-sign)wpi.wpi.edu, elkies(at-sign)abel.math.harvard.edu, emann(at-sign)fas.harvard.edu, nate(at-sign)research.att.com, moorthy(at-sign)cs.rpi.edu, streinu(at-sign)grendel.csc.smith.edu, chung(at-sign)math.upenn.edu, jalfano(at-sign)eve.assumption.edu, bkitchens(at-sign)wesleyan.edu, hochberg(at-sign)math.rutgers.edu, jah(at-sign)christa.unh.edu, romanik(at-sign)dimacs.rutgers.edu, lenhart(at-sign)cs.williams.edu, sheila(at-sign)paris-gw.cs.miami.edu, pavol(at-sign)cs.sfu.ca, wantland(at-sign)mcs1.wcsu.ctstateu.edu, ross(at-sign)cs.amherst.edu, kia(at-sign)oregano.unh.edu, simion(at-sign)gwuvm.bitnet, innes(at-sign)cs.uri.edu, mcrystal(at-sign)bbn.com, finizio(at-sign)uriacc.uri.edu, macula(at-sign)geneseo.bitnet, kcirino(at-sign)lynx.dac.neu.edu, propp(at-sign)math.mit.edu, rstan(at-sign)math.mit.edu, combinatorics(at-sign)math.mit.edu, k.p.bogart(at-sign)dartmouth.edu, sdc(at-sign)cs.albany.edu, peterrc(at-sign)wpi.wpi.edu, kcollins(at-sign)eagle.wesleyan.edu, rhaas(at-sign)smith.smith.edu, lrose(at-sign)sallie.WELLESLEY.EDU, jjr(at-sign)linus.mitre.org, sandifer(at-sign)wcsub.ctstateu.edu, orourke(at-sign)sophia.smith.edu, senechal(at-sign)minkowski.smith.edu, immerman(at-sign)freya.cs.umass.edu, ccm(at-sign)cs.amherst.edu, diwan(at-sign)freya.cs.umass.edu, girkar(at-sign)freya.cs.umass.edu, grupen(at-sign)freya.cs.umass.edu, guruvado(at-sign)cs.umass.edu, herbordt(at-sign)cs.umass.edu, krithi%nirvan(at-sign)cs.umass.edu, lam(at-sign)cs.amherst.edu, liu(at-sign)freya.cs.umass.edu, lory(at-sign)freya.cs.umass.edu, atrenk(at-sign)sallie.WELLESLEY.EDU, landau(at-sign)freya.cs.umass.edu, malitz%oahu(at-sign)cs.umass.edu, rsnbrg(at-sign)freya.cs.umass.edu, adean(at-sign)skidmore.edu, jzca(at-sign)marist.bitnet, FRANZBLA(at-sign)dimacs.rutgers.edu, jhs(at-sign)math.cornell.edu, kamck(at-sign)mvax.cc.conncoll.edu, albertson(at-sign)smith.smith.edu, llangley(at-sign)carbon.denver.colorado.edu, Tom.Sundquist(at-sign)dartmouth.edu, rajpal(at-sign)griggs.dartmouth.edu, dbeers(at-sign)vmsvax.simmons.edu, bennett(at-sign)math.umass.edu, fishel(at-sign)scsud.ctstateu.edu, gptesler(at-sign)euclid.ucsd.edu, streinu(at-sign)sophia.smith.edu, eaton(at-sign)cs.uri.edu, susan(at-sign)max.math.brandeis.edu, archdeac(at-sign)uvm-gen.emba.uvm.edu, kenney(at-sign)siena.bitnet, hutchinson(at-sign)macalstr.edu, lovasz-laszlo(at-sign)cs.yale.edu, plock(at-sign)stlawu.bitnet, dvella(at-sign)skidmore.edu, kwong(at-sign)mary.cs.fredonia.edu, lbutler(at-sign)acc.haverford.edu, jsims(at-sign)eagle.wesleyan.edu, ecoven(at-sign)eagle.wesleyan.edu, jlewis(at-sign)uriacc.uri.edu, sanjoy(at-sign)emba.uvm.edu, rjyanco(at-sign)unix.amherst.edu, gara(at-sign)emba.uvm.edu, ravi(at-sign)cs.uri.edu, quintas(at-sign)pacevm.dac.pace.edu, kennedyf(at-sign)pacevm.dac.pace.edu, lfeng(at-sign)eagle.wesleyan.edu, ssilberger(at-sign)eagle.wesleyan.edu, bheiles(at-sign)eagle.wesleyan.edu, krg(at-sign)rover.wellesley.edu, Rhoades(at-sign)emmy.smith.edu, hull(at-sign)cs.uri.edu, rajpal(at-sign)dartmouth.edu, "silbergd(at-sign)snynewvm.bitnet X-Envelope-To":apost(at-sign)math.mit.edu, ariki(at-sign)math.mit.edu, bona(at-sign)math.mit.edu, cathan(at-sign)math.mit.edu, combinatorics(at-sign)math.mit.edu, dfinberg(at-sign)math.mit.edu, djk(at-sign)math.mit.edu, fomin%(at-sign)math.mit.edu, lpachter(at-sign)math.mit.edu, mshimo(at-sign)math.mit.edu, propp(at-sign)math.mit.edu, rstan(at-sign)math.mit.edu, sara(at-sign)math.mit.edu, satomi(at-sign)math.mit.eduSubject:Smith College One day conference participants

Mike Albertson Smith College Northampton, MA 01063 413-585-3865 Albertson(at-sign)smith.smith.edu Joseph A. Alfano Assumption College Department of Mathematics 500 Salisbury Street Worcester, MA 01615-0005 (508) 767-7561 jalfano(at-sign)eve.assumption.edu Kenneth Appel University of New Hampshire Department of Mathematics, Kingsbury Hall, Durham NH 03824 (603) 862-2673 kia(at-sign)oregano.unh.edu Dan Archdeacon The University of Vermont 16 Colchester Ave Burlington VT 05405 802-656-0850 dan.archdeacon(at-sign)uvm.edu Sanjoy Baruah The University of Vermont Dept of CS&EE, 351 Votey Building The University of Vermont Burlington, Vt 05405. (802)656-2547. sanjoy(at-sign)cs.uvm.edu Donna Beers Mathematics Department Simmons College Boston, MA 02115 617-521-2389 dbeers(at-sign)vmsvax.simmons.edu M. K. Bennett U. Mass. Department of Mathematics and Statistics University of Massachusetts Amherst, MA 01003 413-549-0545 bennett(at-sign)math.umass.edu Andrew Beveridge Department of Mathematics Yale University New Haven, CT 06520 beveridg(at-sign)pascal.math.yale.edu Ken Bogart Dartmouth College Mathematics Department 6188 Bradley Hall Hanover, NH 03755-3551 603-646-3178 k.p.bogart(at-sign)dartmouth.edu Lynne M. Butler Haverford College Department of Mathematics Stokes Hall Haverford College Haverford, PA 19041 (610) 896-1300 office (610) 642-7877 home lbutler(at-sign)haverford.edu Seth Chaiken SUNY at Albany Computer Science Department LI-67A SUNY at Albany Albany, NY 12222 518-442-4282 sdc(at-sign)cs.albany.edu Peter R.Christopher Worcester Polytechnic Institute Worcester,MA 01609 508-831-5269 peterrc(at-sign)wpi.edu Kristine Cirino Northeastern University Department of Mathematics Northeastern University Boston, MA 02115 (617)373-2450 kcirino(at-sign)lynx.neu.edu Karen L. Collins Wesleyan University Department of Mathematics Middletown CT 06459-0128 (203) 685-2169 kcollins(at-sign)wesleyan.edu Ethan M. Coven Wesleyan University Department of Mathematics Wesleyan University Middletown, CT 06459-0128 203-685-2204 ecoven(at-sign)wesleyan.edu Lenore Cowen Johns Hopkins University Dept. of Math. Sciences, Maryland Hall, JHU, Baltimore, MD 21218 (410) 516-7043 cowen(at-sign)brutus.mts.jhu.edu Alice M. Dean Skidmore College Mathematics and Computer Science Department Saratoga Springs, NY 12866 518-584-5000, ext. 2371 adean(at-sign)skidmore.edu Nathaniel Dean AT&T Bell Laboratories Room 2C-415 600 Mountain Avenue Murray Hill, NJ 07974 Phone: 908-582-4190 Fax: 908-582-7550 nate(at-sign)research.att.com Nancy Eaton Department of Mathematics University of Rhode Island Kingston, RI 02881 (401) 792-4439 eaton(at-sign)math.uri.edu Li Feng Department of Mathematics Wesleyan University Middletown CT 06459 (203)685-2165 LFENG(at-sign)EAGLE.WESLEYAN.EDU Norman J. Finizio University of Rhode Island Department of Mathematics, URI, Kingston, RI 02881 (401) 792-4430 finizio(at-sign)uriacc.uri.edu Susanna Fishel Southern Connecticut State University Math Department SCSU 501 Crescent Ave New Haven, CT 06515 (203) 397-5579 office fishel(at-sign)scsud.ctstateu.edu Deborah S. Franzblau Rutgers University DIMACS, PO Box 1179, Piscataway NJ 08855 908-445-4573 franzbla(at-sign)dimacs.rutgers.edu Richard Goldstone Department of Mathematics Marist College 290 North Road Poughkeepsie, NY 12601 richard.goldstone(at-sign)marist.edu work phone: (914) 575-3000 x2613 home phone: (914) 473-3797 Ruth Haas Smith College Department of Mathematics, Northampton, MA 01063 (413) 585-3872 rhaas(at-sign)smith.smith.edu Barbara Heiles Wesleyan University Math Dept, Wesleyan University Middletown, CT 06459 (203)685-2167 bheiles(at-sign)wesleyan.edu Jeffrey Allan Hall Department of Mathematics University of New Hampshire Durham, NH 03824 (603) 862-2715 http://www.math.unh.edu/~jah jah(at-sign)spicerack.unh.edu Pavol Hell Simon Fraser University School of Computing Science, SFU, Burnaby, B.C., Canada V5A1S6 604-291-3391 pavol(at-sign)cs.sfu.ca Thomas Hull Dept. of Mathematics University of Rhode Island Kingston, RI 02881-0816 Joan P. Hutchinson Macalester College Department of Mathematics and Computer Science, Macalester College, St. Paul MN 55105 612-696-6134 hutchinson(at-sign)macalstr.edu Duncan Innes University of Rhode Island 134 Graduate Village (401) 792-4223 innes(at-sign)cs.uri.edu Robert E. Jamison Department of Mathematical Sciences Clemson University Clemson, SC 29634-1907 rejam(at-sign)clemson.edu OFFICE: (803) 656-5219 FAX: (803) 656-5230 Emelie Kenney Department of Mathematics Siena College Loudonville, NY 12211 (518) 783-2913 kenney(at-sign)siena.edu John W. Kennedy Department of Mathematics Pace University Pace Plaza New York, NY 10038 (718)224-8595 kennedyf(at-sign)pacevm.dac.pace.edu Susan Landau UMass Computer Science, UMass, Amherst, MA 01003 413-545-0263 landau(at-sign)cs.umass.edu Jim Lewis Univ. of R.I. Math Dept, Tyler Hall Kingston, RI 02881 792-4430 jlewis(at-sign) uriacc.uri.edu Yanxi Liu University of Mass. 15 Kennedy Drive Hadley, MA 01035 413-545-2303 (O) 413-549-6911 (H) liu(at-sign)cs.umass.edu Patti Frazer Lock St. Lawrence University Dept. of Mathematics St. Lawrence University Canton, NY 13617 315-379-5292 plock(at-sign)vm.stlawu.edu Laszlo Lovasz Yale University, Dept. of Computer Science New Haven, CT 06520 203-432-1245 lovasz(at-sign)cs.yale.edu Ross McConnell Amherst College Department of Math and Computer Science, Amherst College, Amherst, MA 01002 (413)-542-7913 ross(at-sign)cs.amherst.edu Cathy McGeoch Amherst College Amherst, MA 01002 413-542-2414 (For now; will change in 2 weeks) ccm(at-sign)cs.amherst.edu Kathy McKeon Connecticut College Conn College Box 5561 270 Mohegan Ave New London, CT 06320-4196 203-439-2012 kamck(at-sign)conncoll.edu Sergio Rajsbaum MIT Laboratory for Computer Science, NE43-367 545 Technology Square Cambridge, MA 02139 Ph: (617) 253 5905 (617) 623 3325 (home) Fax:(617) 253 3480 E-mail: rajsbaum at theory.lcs.mit.edu Donald Silberger Department of Mathematics & Computer Science State University of New York New Paltz, NY 12561 Phones: (914)-257-3557 (at SUNY) -255-8819 (at home) E-mail: SILBERGD(at-sign)NPVM.NEWPALTZ.EDU Sylvia Silberger Wesleyan University Math Dept. Wesleyan University Middletown, CT 06459 (203)685-2167 SSilberger(at-sign)eagle.wesleyan.edu Gara Pruesse Dept of Computer Science and Electrical Engineering Votey Building University of Vermont Burlington, VT 05405-0156 (802) 656-2538 office (802) 656-0696 fax e-mail: gara(at-sign)cs.uvm.edu Louis V. Quintas Pace University Mathematics Department, New York, NY 10038 Phone: (212) 346 1280 e-mail Address: quintas(at-sign)pacevm.dac.pace.edu Kathleen Romanik DIMACS Center for Discrete Mathematics and Theoretical Computer Science Rutgers University P.O. Box 1179 Piscataway, NJ 08855-1179 (908) 445-4576 romanik(at-sign)dimacs.rutgers.edu Lauren Rose Wellesley College Math Department/Science Center Wellesley College Wellesley, MA 02181 phone number: 617-283-3114 e-mail address: lrose(at-sign)wellesley.edu or lrose(at-sign)molly.wellesley.edu Arnold L. Rosenberg University of Massachusetts Department of Computer Science Amherst, MA 01003 413/545-2743 rsnbrg(at-sign)cs.umass.edu Joe J. Rushanan The MITRE Corporation, MS E025 202 Burlington Road Bedford, MA 01730-1420 (617) 271-2320 jjr(at-sign)mitre.org Ed Sandifer Western Connecticut State University Math/CS Department Danbury, CT 06810 (203) 426-5326 sandifer(at-sign)wcsu.ctstateu.edu rodica simion dept of mathematics george washington university washington, dc 20052 (202) 994 6238 simion(at-sign)gwuvm.gwu.edu Richard Stanley MIT Department of Mathematics 2-375 Cambridge, MA 02139 (617) 253-7930 rstan(at-sign)math.mit.edu Ileana Streinu Computer Science Department Smith College Northampton, MA 01063 Phone: 413-585-3827 email: streinu(at-sign)cs.smith.edu Thomas Sundquist Dartmouth College HB 6188, Hanover NH, 03755 (603) 646-1590 Tom.Sundquist(at-sign)dartmouth.edu Steve Tanny Department of Mathematics University of Toronto Toronto, Ontario Canada M5S 1A1 tanny(at-sign)math.toronto.edu Ann Trenk Mathematics Department Wellesley College Wellesley, MA 02181 (617) 283-3140 atrenk(at-sign)wellesley.edu [On sabbatical at DIMACS in 95-96. Email will be forwarded.] David C. Vella Skidmore College Dept. Mathematics & Computer Science Saratoga Springs, NY 12866 518-584-5000; ext. 2364 dvella(at-sign)skidmore.edu Kati Vesztergombi Yale University, Dept. of Mathematics New Haven, CT 06520 203-432-4682 kati(at-sign)math.yale.edu Evan Wantland Dept of Math and CS WCSU 181 White St Danbury, CT 06810 203 837 9355 wantland(at-sign)mcs1.wcsu.ctstateu.edu

Date:Wed, 15 Nov 1995 11:04:40 -0500 (EST)From:Sergey Fomin <fomin(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Kalai, 11/20

APPLIED MATHEMATICS COLLOQUIUM SPEAKER: Gil Kalai Institute for Advanced Study and Hebrew University TOPIC: All Monotone Graph Properties Have Sharp Thresholds ABSTRACT: In their seminal work which initiated random graph theory Erd\"os and R\'enyi discovered that many graph properties have sharp thresholds as the number of vertices tends to infinity. That is, if every edge of the graph is chosen with probability $p$, then when $p$ increases, the transition from a property being very unlikely to its being very likely is very swift. We prove a conjecture of Linial that every monotone graph property has a sharp threshold. This result applies to random subgraphs of arbitrary symmetric graphs. We will discuss the relation between the symmetry group and the length of the transition interval. DATE: Monday, November 20, 1995 TIME: 4:15 p.m. LOCATION: Building 2 -- Room 105 REFRESHMENTS WILL BE SERVED FROM 3:45 P.M. IN BUILDING 2, ROOM 349.

Date:Fri, 17 Nov 1995 10:58:26 -0500From:kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)Subject:spring dates and websiteTo:kcollins(at-sign)MAIL.WESLEYAN.EDU

Dear CONE mailing list, We have set the dates for the spring meetings at Smith College. They are: Sunday, February 4, 1996 Saturday, March 30, 1996 Saturday, April 27, 1996 The speakers for the February 4th meeting will be: Ethan Coven, Danny Kleitman, Emily Petrie, and Joe Rushanan. We will send out an announcement with titles in early January. We now have a Website for the CONE meetings. The address is http://math.smith.edu/~rhaas/coneweb.html The table of contents of the Web site is: dates of future meetings, schedule for next meeting, directions to Smith College, schedules of past meetings, abstracts of talks, papers available electronically, names and addresses of participants, other websites of interest to combinatorists, and the Smith College Mathematics Department page. We hope you will find it useful.

Date:Mon, 20 Nov 1995 22:18:42 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Free-for-all, 11/29

Wednesday, November 29, 4:35 p.m.; MIT, room 2-338 All of Us (from All Over the Boston Area) Open Mike Session / Combinatorial Free-for-All Here's another chance to share partial results, open questions, and nice ideas that aren't suited to the 50-minute talk format. Presenters will include Gian-Carlo Rota, Dan Kleitman, and Christos Athanasiadis. Let Jim Propp know ahead of time what you're bringing, if you plan on presenting something that will take longer than five minutes (propp(at-sign)math.mit.edu; 253-6544).

Date:Mon, 20 Nov 1995 22:20:54 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:MIT Combinatorics Seminar: December schedule

MIT COMBINATORICS SEMINAR Here is a list of talks currently scheduled for the month of December. Notice that talks scheduled on *Wednesdays* will begin at *4:35* p.m., but that talks scheduled on *Fridays* will begin at *4:15*. Wednesday, December 6, 4:35 p.m.: Gian-Carlo Rota, A formal theory of resultants, I: The Cliffordization of Hopf algebras Friday, December 8, 4:15 p.m.: Gian-Carlo Rota, A formal theory of resultants, II: Explicit formulas for resultants Wednesday, December 13, 4:35 p.m.: Heidi Burgiel, Symmetric embeddings of regular maps: regular skew polyhedra All talks will meet in room 2-338.

Date:Fri, 1 Dec 1995 00:41:05 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Rota, 12/6 *and* 12/8

Wednesday, December 6, 4:35 p.m.; MIT, room 2-338 *and* Friday, December 8, 4:15 p.m.; MIT, room 2-338 Gian-Carlo Rota (MIT) A formal theory of resultants Part I: The Cliffordization of Hopf algebras Part II: Explicit formulas for resultants A formula for the resultant of n homogoneous polynomials will be given. This formula can be used to derive all known properties of resultants without recourse to elimination theory. Those who attend are expected to know basic notation of Hopf algebras.

Date:Wed, 6 Dec 1995 08:00:19 -0500 (EST)From:Jim Propp <propp(at-sign)math.mit.edu>To:combinatorics(at-sign)math.mit.eduSubject:Burgiel, 12/13 (last meeting of semester)

Wednesday, December 13, 4:35 p.m.; MIT, room 2-338 Heidi Burgiel (Geometry Center) Symmetric embeddings of regular maps: regular skew polyhedra The label "regular polytope" can be applied to objects ranging from Platonic solids to simplicial complexes. The object of this talk is to describe methods of taking regular maps --- regularly tiled 2-manifolds --- and embedding the vertices of the tilings in Euclidean space to form objects called regular skew polyhedra. These polyhedra have all the symmetries dictated by the automorphism group of the underlying manifold, but may not have planar faces. They need not even lie in three dimensional space! For example, a sphere can be regularly tiled with pentagons. One realization of this map is the dodecahedron. More interestingly, a torus can be tiled with squares. As Coxeter and Petrie discovered in 1926, this map can be realized in four dimensions as a polyhedral surface with square faces and "skew square" vertex figures. In my talk I will describe more skew polyhedra, and review the methods I used to discover them. These methods, involving association schemes and representation theory, can be extended to provide symmetric realizations of any graph or polytope whose automorphism group is vertex-transitive.