Date:           Wed, 10 Jan 1996 17:40:22 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

               Come to the eighteenth one day conference on

                     Combinatorics and Graph Theory

                      *SUNDAY*, February 4, 1996

                         10 a.m. to 4:30 p.m.
                                  at
                            Smith College
                         Northampton MA 01063

                               Schedule

10:00  Ethan Coven (Wesleyan Univ.)
        Tiling the Integers with One Prototile

11:10  Daniel Kleitman (MIT)
        TBA

12:10  Lunch

 2:00  Emily Petrie (Merrimack College)
        The Symmetry Group of an Almost Perfect One-Factorization

 3:10  Joseph J. Rushanan (MITRE)
        Parallel Processing and Cayley 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

-------------------------------------------------------------
Department of Mathematics, Wesleyan University, Middletown CT 06459-0128,
Office: (860) 685-2169, Fax: (860) 685-2571
-------------------------------------------------------------

Date:           Fri, 26 Jan 1996 16:09:48 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

               Come to the eighteenth one day conference on

                     Combinatorics and Graph Theory

                      *SUNDAY*, February 4, 1996

                         10 a.m. to 4:30 p.m.
                                  at
                            Smith College
                         Northampton MA 01063

                               Schedule

10:00  Ethan Coven (Wesleyan Univ.)
        Tiling the Integers with One Prototile

11:10  Daniel Kleitman (MIT)
        Two Problems in Applied Graph Theory:  a Vector Matching
         Problem, and a Shuffling Problem

12:10  Lunch

 2:00  Emily Petrie (Merrimack College)
        The Symmetry Group of an Almost Perfect One-Factorization

 3:10  Joseph J. Rushanan (MITRE)
        Parallel Processing and Cayley 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:           Tue, 30 Jan 1996 19:08:02 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        MIT Combinatorics Seminar: February schedule

		    MIT COMBINATORICS SEMINAR

Here is a list of talks currently scheduled for the month of February.
Notice that talks will normally begin at 4:15 p.m.; however, Vershik's
talk on the 28th (jointly sponsored by the Lie group seminar) will
start at 4:30.

Wednesday, February 7, 4:15 p.m.: Andrei Okounkov,
	Edrei's theorem and representations of S(\infty)  (part I)

Friday, February 9, 4:15 p.m.: Andrei Okounkov,
	Edrei's theorem and representations of S(\infty)  (part II)

Wednesday, February 14, 4:15 p.m.: Igor Pak,
	A new bijective proof of the hook-length formula

Friday, February 23, 4:15 p.m.: Morris Dworkin,
	Factorization of the cover polynomial

Wednesday, February 28, 4:30 p.m.: Anatoly Vershik,
	A new version of the representation theory of Coxeter Groups
	and spectra of Gel'fand-Zetlin algebras

All talks will meet in room 2-338.

Date:           Tue, 30 Jan 1996 19:59:13 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Okounkov, 2/7 and 2/9

Wednesday, February 7 and Friday, February 9, 4:15 p.m.; MIT, room 2-338

		Andrei Okounkov (Institute for Advanced Study)

	       Edrei's theorem and representations of S(\infty)

Abstract: 

Edrei's theorem describes all so-called totally positive (or Polya 
frequency) sequences.  By definition, a sequence  (a_i)  is called 
totally positive if
	\det [a_{i_p j_q}]_{1 \le p,q \le k}
for all k greater than or equal to 0 and all
	i_1 < i_2 < ...  < i_k, 
	j_1 < j_2 < ... < j_k .
Such sequences arise in approximation theory, probability, ..., and 
representation theory of S(\infty), U(\infty), O(\infty), Sp(\infty).  
Two proofs of this theorem were known: Edrei's original proof, 
based on results of Nevanlinna about entire functions, and the 
``ergodic'' proof of Vershik and Kerov, based on the calculation
of the asymptotics of the characters of S(n) as n goes to infinity.
New methods in the representation theory of infinite-dimensional
classical groups provide a new proof of Edrei's theorem as well as
a remarkable simplification of the existing proofs.

Date:           Wed, 31 Jan 1996 18:08:51 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

This is just to remind everyone who might attend the February 4th
CONE conference, that for the first time the conference is meeting
on a SUNDAY.

The spring conferences in March and April will both be on SATURDAY.

Date:           Thu, 1 Feb 1996 22:12:00 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Talk by Zelevinsky at Northeastern

  The following talk may be of interest to combinatorialists:

  Monday Feb 5 at Northeastern's Geometry-Algebra-Singularities Seminar:
     
     Andrei Zelevinsky:  "Totally positive matrices and pseudo line
                          arrangements"

     1:30 PM at 509 Lake Hall.

Date:           Wed, 7 Feb 1996 13:20:18 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Pak, 2/14

Wednesday, February 14 1, 4:15 p.m.; MIT, room 2-338

		      Igor Pak (Harvard)

        A new bijective proof of the hook-length formula
 

We present a new proof of the hook-length formula for the dimension of 
the irreducible representation of the symmetric group.  In order to do 
that we construct an explicit bijection between two sets of tableaux. 

Those who are interested may refer to 
	http://www.labri.u-bordeaux.fr/~betrema/pak/pak.html
for definitions and nice examples.

Date:           Fri, 16 Feb 1996 12:14:52 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Dworkin, 2/23

Friday, February 23, 4:15 p.m.; MIT, room 2-338

		Morris Dworkin (Brandeis)

	 Factorization of the cover polynomial
 

Chung and Graham's cover polynomial generalizes Goldman, Joichi, 
and White's "factorial" rook polynomial to two variables.  We factor 
the cover polynomial completely for Ferrers boards with either 
increasing or decreasing column heights.  For column permuted 
Ferrers boards, we find a sufficient condition for its partial 
factorization.  We apply this to column permuted "staircase boards," 
getting a partial factorization in terms of the column permutation, 
as well as a sufficient condition for complete factorization.

Date:           Wed, 21 Feb 1996 01:40:30 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Vershik, 2/28

Wednesday, February 28, 4:30 p.m.; MIT, room 2-338

	      Anatoly Vershik (Steklov Mathematical Institute)

	A new version of the representation theory of Coxeter Groups 
                  and spectra of Gel'fand-Tsetlin algebras

Classical representation theory of the symmetric groups (Young, Frobenius, 
Schur, Weyl, von Neumann, et al.) involves from the outset the notion of 
Young diagrams and some nontrivial combinatorics of the Young lattice. 

Since the branching rule for the irreducible representations of S_n 
(n=1,2,...) is described by the Young lattice, one could wonder: is it 
possible to find this rule a priori, i.e., before all the representation 
theory of S_n is constructed?  For beginners, the "yes" answer would 
justify the introduction of the Young diagrams, whereas the experts 
could say that the representation theory of the symmetric groups at last
(a century after its creation) becomes a part of general representation 
theory.

Now we can say "yes"!  Using Coxeter generators, Murphy-Jusys elements, 
Gel'fand-Tsetlin subalgebra for the symmetric groups, its spectrum, 
and adding some simple arguments, we obtain a new and very natural 
version of this remarkable classical theory. 

Date:           Fri, 23 Feb 1996 14:31:26 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Re: Vershik, 2/28 (starting time)

This is a reminder that Vershik's talk this coming Wednesday ("A new 
version of the representation theory of Coxeter Groups and spectra of 
Gel'fand-Tsetlin algebras") will begin at *4:30* (not the usual 4:15), 
since it is being sponsored jointly with the Lie Groups seminar.

Date:           Fri, 23 Feb 1996 15:55:45 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Vershik talk, 2/29

The following talk may be of interest to local combinatorialists:

Anatoly Vershik,
Joint Brandeis-Harvard-MIT-Northeastern Colloquium,
Feb. 29, 4:30pm, Room 335, New Classroom Building,
Northeastern University (tea at 4pm in Room 509, Lake Hall):
"Asymptotic combinatorial and geometric problems from the statistical 
physics point of view."

Date:           Sun, 25 Feb 1996 15:05:25 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Cohn and Propp, 3/1

Friday, March 1, 4:15 p.m.; MIT, room 2-338

		Henry Cohn (Harvard) and Jim Propp (M.I.T.)

		A limit law for constrained plane partitions

MacMahon showed that the number of plane partitions with at most n rows, 
at most n columns, and all parts of size at most n is equal to

                     n-1     n-1     n-1
                   ------- ------- -------
                    |   |   |   |   |   |   i+j+k+2
                    |   |   |   |   |   |   --------
                    |   |   |   |   |   |   i+j+k+1
                     i=0     j=0     k=0

(a generalization of binomial coefficients).  The problem can also be
viewed as one of counting plane partitions whose solid Young diagram 
fits inside an n-by-n-by-n box, or as one of counting tilings of a 
regular hexagon of side-length n by rhombuses of side 1.

Working with Michael Larsen, we have recently shown that for n large, 
a ``typical'' tiling of the hexagon (i.e., one chosen uniformly at 
random from the set of all tilings with n fixed) has one sort of
behavior near the boundary of the hexagon and a qualitatively different 
sort in the interior, where the border between the two regions is 
asymptotically given by the circle inscribed in the hexagon.  The
local behavior inside the circle varies from place to place, and we
can give a formula for how it varies.  Our results can be interpreted
as giving an asymptotic law for the typical shape of the solid Young
diagram of a constrained plane partition.

Date:           Sun, 25 Feb 1996 19:44:06 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
Subject:        April 27th CoNE meeting
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

The twentieth meeting of the CoNE conferences will be held
Saturday, April 27, 1996.  To celebrate, we are planning both
a problem session in place of the usual 11:10 talk, with a
pizza lunch ($5 per person) directly following.

If you would like to submit one or more problems, please send
a short written description of the problem(s) to

Mike Albertson (albertson(at-sign)smith.smith.edu)

on or before Thursday, April 25th.  TeX is OK, as is ASCII, or even
hard copy (to Clark Science Center, Smith College, Northampton MA 01063),
but please keep each problem on one page.  Printed versions of these
descriptions will be handed out to the participants at the meeting.  We'll
schedule problem submitters in the problems session for 5-10 minutes each.

There will be a sign up for the pizza lunch at the meeting on Saturday,
before and directly after the 10:00 talk.  Thanks, and we hope to see
you there.

Date:           Sun, 25 Feb 1996 19:51:01 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
Subject:        April 27th CoNE meeting
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

The twentieth meeting of the CoNE conferences will be held
Saturday, April 27, 1996.  To celebrate, we are planning both
a problem session in place of the usual 11:10 talk, with a
pizza lunch ($5 per person) directly following.

If you would like to submit one or more problems, please send
a short written description of the problem(s) to

Mike Albertson (albertson(at-sign)smith.smith.edu)

on or before Thursday, April 25th.  TeX is OK, as is ASCII, or even
hard copy (to Clark Science Center, Smith College, Northampton MA 01063),
but please keep each problem on one page.  Printed versions of these
descriptions will be handed out to the participants at the meeting.  We'll
schedule problem submitters in the problems session for 5-10 minutes each.

There will be a sign up for the pizza lunch at the meeting on Saturday,
before and directly after the 10:00 talk.  Thanks, and we hope to see
you there.

Date:           Sun, 25 Feb 1996 19:58:16 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
Subject:        April 27th CoNE meeting
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

The twentieth meeting of the CoNE conferences will be held
Saturday, April 27, 1996.  To celebrate, we are planning both
a problem session in place of the usual 11:10 talk, with a
pizza lunch ($5 per person) directly following.

If you would like to submit one or more problems, please send
a short written description of the problem(s) to

Mike Albertson (albertson(at-sign)smith.smith.edu)

on or before Thursday, April 25th.  TeX is OK, as is ASCII, or even
hard copy (to Clark Science Center, Smith College, Northampton MA 01063),
but please keep each problem on one page.  Printed versions of these
descriptions will be handed out to the participants at the meeting.  We'll
schedule problem submitters in the problems session for 5-10 minutes each.

There will be a sign up for the pizza lunch at the meeting on Saturday,
before and directly after the 10:00 talk.  Thanks, and we hope to see
you there.

Date:           Sun, 25 Feb 1996 19:52:57 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
Subject:        April 27th CoNE meeting
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

The twentieth meeting of the CoNE conferences will be held
Saturday, April 27, 1996.  To celebrate, we are planning both
a problem session in place of the usual 11:10 talk, with a
pizza lunch ($5 per person) directly following.

If you would like to submit one or more problems, please send
a short written description of the problem(s) to

Mike Albertson (albertson(at-sign)smith.smith.edu)

on or before Thursday, April 25th.  TeX is OK, as is ASCII, or even
hard copy (to Clark Science Center, Smith College, Northampton MA 01063),
but please keep each problem on one page.  Printed versions of these
descriptions will be handed out to the participants at the meeting.  We'll
schedule problem submitters in the problems session for 5-10 minutes each.

There will be a sign up for the pizza lunch at the meeting on Saturday,
before and directly after the 10:00 talk.  Thanks, and we hope to see
you there.

Date:           Mon, 26 Feb 1996 09:34:04 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
Subject:        April 27th CoNE meeting
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

The twentieth meeting of the CoNE conferences will be held
Saturday, April 27, 1996.  To celebrate, we are planning both
a problem session in place of the usual 11:10 talk, with a
pizza lunch ($5 per person) directly following.

If you would like to submit one or more problems, please send
a short written description of the problem(s) to

Mike Albertson (albertson(at-sign)smith.smith.edu)

on or before Thursday, April 25th.  TeX is OK, as is ASCII, or even
hard copy (to Clark Science Center, Smith College, Northampton MA 01063),
but please keep each problem on one page.  Printed versions of these
descriptions will be handed out to the participants at the meeting.  We'll
schedule problem submitters in the problems session for 5-10 minutes each.

There will be a sign up for the pizza lunch at the meeting on Saturday,
before and directly after the 10:00 talk.  Thanks, and we hope to see
you there.

Date:           Fri, 1 Mar 1996 12:31:13 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Carroll, 3/6 (special meeting)

SPECIAL MEETING OF THE COMBINATORICS SEMINAR

Wednesday, March 6, 3:00 p.m.; MIT, room 2-338
                    ^^^^^^^^  (note unusual time)

		    Sean Carroll (M.I.T.)

	Beyond matrix models: a combinatorial approach 
	to discretized two-dimensional quantum gravity
 

The Feynman path integral for two-dimensional quantum gravity, which 
is a sum over geometries and matter configurations, can be calculated 
by taking the continuum limit of a discretized theory of triangulated 
surfaces with combinatorial data representing matter fields.  I will 
discuss an approach to such a calculation using recursion equations 
in free variables.  The flexibility of this method allows the computation 
of a number of quantities which would be difficult to compute using
traditional "matrix model" approaches to these theories.

Date:           Fri, 1 Mar 1996 12:37:45 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        *** CHANGE OF SCHEDULE ***

Emily Petrie's talk, which was announced for March 6, will be given on March 8.
There isn't time to send out mail about this, so please spread the word to
anyone you know who you think might be planning to attend her lecture.

A corrected announcement for her talk follows.

Jim Propp

Date:           Fri, 1 Mar 1996 12:38:39 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Petrie, 3/8

Friday, March 8, 4:15 p.m.; MIT, room 2-338
        ^^^^^^^ (note change of date)

			Emily Petrie (Merrimack)

	The symmetry group of an almost perfect one-factorization

A perfect 1-factorization of the complete graph K2n may be defined
as a partition of the edge set into 1-factors, such that the union of 
any two of the 1-factors is connected.  When viewed this way, a natural
generalization is to consider 1-factorizations of K2n where the union of
any three of the 1-factors is connected.  We call these almost perfect
1-factorizations.  We examine the automorphism group G of such
1-factorizations.  For perfect 1-factorizations on K2n,  strong
divisibility conditions have been established for the size of the
automorphism group, depending only on n.  However for other types of
1-factorizations the order of the automorphism group can be relatively
large in comparison with the number of vertices 2n.  We ask, what
restrictions can be placed on the size of the automorphism group G in 
the case of an almost perfect 1-factorization?

Date:           Fri, 1 Mar 1996 13:55:20 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        MIT Combinatorics Seminar: March schedule

Here is a list of talks currently scheduled for the month of March.
Notice that all talks will begin at 4:15 p.m. except for the talk
on March 6.

Friday, March 1, 4:15 p.m.: Henry Cohn and Jim Propp,
	A limit law for constrained plane partitions

Wednesday, March 6, 3:00 p.m.: Sean Carroll,
	Beyond matrix models: a combinatorial approach to discretized 
	two-dimensional quantum gravity

Friday, March 8, 4:15 p.m.: Emily Petrie,
	The symmetry group of an almost perfect one-factorization 

Wednesday, March 13, 4:15 p.m.: Alex Postnikov,
	Deformed Coxeter hyperplane arrangements 

Friday, March 15, 4:15 p.m.: Christos Athanasiadis,
	The characteristic polynomial of a rational subspace arrangement 

Wednesday, March 20, 4:15 p.m.: Volkmar Welker,
	On divisor posets of affine semigroups

All talks will meet in room 2-338.

Date:           Mon, 4 Mar 1996 19:48:53 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Discrete Dinner: preliminary announcement

It's time to start planning the spring semester's Discrete Dinner.
Please send me comments on the following proposed dates:

Friday, April 12
Wednesday, April 17
Friday, April 19
Wednesday, April 24
Friday, April 26

As usual, I ask you to indicate the strengths of your preferences
for the respective dates (from "impossible" to "strongly preferred").

Jim Propp

Date:           Mon, 4 Mar 1996 19:49:42 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Postnikov, 3/13

Wednesday, March 13, 4:15 p.m.; MIT, room 2-338

		Alex Postnikov (M.I.T.)

	Deformed Coxeter hyperplane arrangements

The braid or Coxeter arrangement of type A_{n-1} is the arrangement of
hyperplanes in R^n given by the equations x_i - x_j = 0.  We study
deformations of this arrangement, i.e., hyperplane arrangements of the
type

x_i - x_j = a_{ij}^1,a_{ij}^2,...,a_{ij}^k.

We calculate the number of regions and the Poincare polynomial for
many arrangements of this form.  In particular, we prove a conjecture
by Richard Stanley that the number of regions of the arrangement in
R^n given by the equations x_i - x_j = 1, i<j, is equal to the number
of alternating trees on {1,2,...,n}.  The number of regions and the
Poincare polynomial have some interesting combinatorial and
arithmetical properties.  Many of the results presented here are
obtained in collaboration with Richard Stanley.

Date:           Mon, 4 Mar 1996 20:11:12 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Athanasiadis, 3/15

Friday, March 15, 4:15 p.m.; MIT, room 2-338

			Christos Athanasiadis (M.I.T.)

	The characteristic polynomial of a rational subspace arrangement
 

Let A be an affine subspace arrangement in R^n, defined over the integers. 
We give a combinatorial interpretation of the characteristic polynomial 
chi(A, q)  of A that is valid for sufficiently large prime values of q. 
This result, which generalizes a theorem of Blass and Sagan, reduces the 
computation of  chi(A, q)  to a counting problem and provides an explanation 
for the wealth of combinatorial results discovered in the theory of 
hyperplane arrangements in recent years.  The basic idea appeared for the 
first time in 1970 in a theorem of Crapo and Rota, which unfortunately 
was overlooked in the later development of the theory of arrangements.

We give applications for various hyperplane arrangements. These include a 
simple, uniform proof of a result of Blass and Sagan about the characteristic 
polynomial of a Coxeter arrangement, simple derivations of the characteristic 
polynomials of the Shi arrangements and various generalizations and a another
proof of Stanley's conjecture about the number of regions of the Linial 
arrangement.  We also extend our method to the computation of all face numbers
of a rational hyperplane arrangement. 

Date:           Mon, 4 Mar 1996 20:29:26 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Re: Discrete Dinner

It's been pointed out to me that two of my proposed dinner dates
(April 17 and April 19) fall during the RotaFest, and I think
that this makes them unsuitable.  So let's restrict ourselves
to considering April 12, 24, and 26 for the time being.

Jim Propp

Date:           Mon, 11 Mar 1996 13:31:47 -0500
From:           kcollins(at-sign)MAIL.WESLEYAN.EDU (Karen L. Collins)
To:             kcollins(at-sign)MAIL.WESLEYAN.EDU

               Come to the nineteenth one day conference on

                     Combinatorics and Graph Theory

                      Saturday, March 30, 1996

                         10 a.m. to 4:30 p.m.
                                  at
                            Smith College
                         Northampton MA 01063

                               Schedule

10:00  Andrew Kotlov (Yale University)
        The rank and chromatic number of graphs

11:10  Rodica Simion (George Washington University)
            Some relations between polytopes and combinatorial statistics

12:10  Lunch

 2:00  Sheila Sundaram (University of Miami)
        On the homology of partitions with an even number of blocks

 3:10  Tamas Szonyi (Yale University)
        Blocking sets in projective planes

*Our three year NSF grant is ending this spring.  Looking at the
remaining budget for the two spring conferences, we have to reduce
the transportation allowance for non-local participants for the
March 30th conference to $40 (from the usual $50).  We have applied
for a renewal for another 3 years of grant support, and hope to hear
soon from NSF.*

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

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:           Tue, 12 Mar 1996 00:26:13 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Discrete Dinner

It seems that many people can't make any of the dates in April, so
I'm considering holding the Discrete Dinner in early May.  I would
appreciate feedback on the following dates:

Wednesday, May 1
Friday, May 3
Wednesday, May 8
Friday, May 10

Jim Propp

Date:           Thu, 14 Mar 1996 15:04:05 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        talk by Boris Shapiro, 3/19

Combinatorialists may be interested in the following seminar:

        Boris Shapiro (U. Stockholm)

   "Enumeration of connected components of the intersection of two open
    opposite Schubert cells"

     Tuesday March 19 at 1 PM, at 509 Lake Hall, Northeastern Univ.
   - Geometry-Algebra-Singularities Seminar -

Following is amsteX abstract:       

\input {amstex}
\advance\voffset  by -1.0cm
\NoBlackBoxes
%\nopagenumbers
\magnification=\magstep1
%\hfuzz=3.5pt
\hsize=17truecm
\vsize=24.2truecm
\voffset=0.5truecm
%\hoffset
\document

\define \bZ {\Bbb Z}

\topmatter
\title
On the number of connected components in the intersection of 2 open
opposite Schubert
cells in $SL_n/B$
\endtitle

\author  B.~Z.~Shapiro, M.~Z.~Shapiro, A.~D.~Vainshtein
\endauthor

\affil \endaffil

\abstract We consider the space

\endabstract
\abstract
Let $T_n$ denote the group of real unitary uppertriangular matrices and
$\Delta_i,\;i=1,...,n-1$
denote the the hypersurface in $T_n$ given by vanishing of the 'principal'
$i\times i$-minor in the
right upper corner.  We study the number of connected components in $\Cal
C_n=T_n
\setminus \bigcup_i\Delta_i$ using ideas from \cite {L} and \cite {BFZ}. At
first the
problem is reduced to a purely combinatorial question about some 'action'
on the group $T_n(\bZ_2)$
of uppertriangular matrices with $0-1$-entries. The final conjecture under
consideration is as follows.
The number $\sharp_n$ of connected components in $\Cal C_n$ equals $3\times
2^n$ for all $n\ge 5$.
(Cases $n=3$ and $n=4$ are exceptional and $\sharp_3=6$, $\sharp_4=52$.)

\endabstract
\endtopmatter

\Refs
\widestnumber \key{ShSh}

\ref \key {BFZ} \by A.~Berenstein, S.~Fomin, A,~Zelevinski
\paper Parametrizations of canonical bases and totally positive matrices
 \jour preprint
\yr 1995\pages 1--98\endref

\ref \key {L} \by G.~Lusztig
\paper Total positivity in reductive groups
\inbook Lie theory and geometry: in honor of Bertram Kostant, Progress in Math
\publ Birkh\"auser\vol 123
\yr 1994
\endref

\ref \key {SS} \by B.~Z.~Shapiro,  M.~Z.~Shapiro
\paper On the totally positive upper triangular matrices
\finalinfo accepted to Lin. Alg. and Appl
\endref

\endRefs

\enddocument

Date:           Thu, 14 Mar 1996 15:05:06 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Welker, 3/20

Wednesday, March 20, 4:15 p.m.; MIT, room 2-338

		Volkmar Welker (Essen, Germany))

          On divisor posets of affine semigroups

In this talk we give a preliminary report on work on posets that occur as
lower intervals in the poset defined on the elements of a sub-semigroup S
of N^n by divisibility within S.  By work of Laudal to compute the
homology of the order complexes over k of these posets is equivalent to
compute Tor_i^R(k,k) for R = k[S].  We will show how to reprove some
known results about Koszul rings using these techniques and show that
the complexes that occur in this context are very closely related to 
complexes that are associated to quotients of polynomial ring by 
monomials of degree 2 (e.g., Stanley-Reisner rings of posets). 

Date:           Tue, 19 Mar 1996 19:01:48 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Exactly Solvable Models

These two items may interest some of you:

                           A SYMPOSIUM ON

         EXACTLY SOLUBLE MODELS IN STATISTICAL MECHANICS:
            HISTORICAL PERSPECTIVES AND CURRENT STATUS

                           MARCH 30-31, 1996

                             to be held at
                  Northeastern University, Boston, MA

The purpose of the symposium is to present historical perspectives 
as well as to assess the current status of the field of soluble
models in statistical mechanics.  Invited speakers include 
R. J. Baxter, D. Fisher, V. F. R. Jones, L. H. Kauffman, E. H. Lieb,
B. M. McCoy, J. H. H. Perk, S. Sachdev, C. A. Tracy, P. Wiegmann, 
and others.  

There will also be a mini-poster session for contributed papers.

For further inquiries please contact fywu(at-sign)neu.edu, king(at-sign)neu.edu, or
circs(at-sign)phyjj4.cas.neu.edu, or write to Ms. M McKeever, Department of 
Physics, Northeastern University, Boston, MA 02115.

******************************************************************

Also: Rodney J.  Baxter is currently giving a course on exactly solvable 
models at Northeastern.  It meets every Wed 11:45 am in Rm 114 DANA 
(physics), except this week, for about 10 weeks.  The lectures started 
two weeks ago (next week's lecture will be #3).

Date:           Fri, 22 Mar 1996 15:23:22 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        MIT Combinatorics Seminar: April schedule

Here is a list of talks currently scheduled for the month of April.
Notice that all talks will begin at 4:15 p.m.

Wednesday, April 3, 4:15 p.m.: Tony Iarrobino,
	The hook algebra

Wednesday, April 10, 4:15 p.m.: Andrei Zelevinsky,
	Quasicommuting families of quantum type Plucker coordinates

Friday, April 12, 4:15 p.m.: Ken Fan,
	Schubert varieties and short braidedness

Wednesday, April 24, 4:15 p.m.: Glenn Tesler,
	Plethystic formulas for the Macdonald q,t-Kostka coefficients

Friday, April 26, 4:15 p.m.: Sinai Robins,
	The Ehrhart polynomial of a lattice polytope

All talks will meet in room 2-338.

Date:           Fri, 22 Mar 1996 15:36:57 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        RotaFest and Umbral Calculus workshop

In case there are any subscribers to this list who aren't aware of the RotaFest
and Umbral Calculus workshop to be held here in mid-April, details can be found 
at the URL http://www-math.mit.edu/~loeb/rotafest.html ; you can also contact
Richard Stanley, who is one of the organizers.

Jim Propp

Date:           Fri, 22 Mar 1996 15:37:27 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Iarrobino, 4/3

Wednesday, April 3, 4:15 p.m.; MIT, room 2-338

		Tony Iarrobino (Northeastern)

		       The hook algebra
 

We had shown that given a natural number n, and a sequence
T = (1,2,3,...,d,t_d,...,t_i,...,t_j) of integers satisfying
t_d \geq t_{d+1} \geq ... \geq t_j  and  \Sigma t_i = n , 
then the lattice P(T) of partitions having diagonal lengths T
is isomorphic to a product  Q(T) = L_d \times ... \times L_j
where each L_i is the lattice of partitions having no more than 
t_i-t_{i+1} rows and 1+t_{i-1}-t_i columns, under inclusion. 
The map D from P(T) to Q(T): P --> Q(P) arises from arranging 
the difference-one hooks of P having hands on the i-diagonal 
into parts according to the number of such hooks having a given 
hand.

It follows that the knowledge of Q_1(P) = Q(P) --- the 
difference-one hooks of P --- determines the difference-a hooks
of T for all a.  In this talk we define difference-a hook partitions 
and describe a composition  Q_a(P) \times Q_b(P) --> Q_{a+b}(P) . 
Thus we define a ``hook difference algebra'' such that  Q_a(P) = 
Q_1(P) \times ... Q_1(P)  (a times).  This algebra is related to 
the ``strand map''  S: Q(T) --> P(T)  that is the inverse of D.

This is joint work with J. Yam\'eogo.

Date:           Mon, 25 Mar 1996 16:47:08 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Discrete Dinner

		        Spring 1996 Boston Area 
		      Discrete Mathematics Dinner
		         (first announcement)

This semester's Discrete Dinner will be held on Wednesday, May 8
at 6 p.m. at Helmand's Restaurant (143 First Street, Cambridge)
between Kendall Square and Lechmere.  The cost will be $10 for 
grad students and undergraduates (alcoholic beverages not included), 
with the rest of us making up the difference.  

Please let me know by May 1 (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, 3 Apr 1996 10:28:27 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Zelevinsky, 4/10

Wednesday, April 10, 4:15 p.m.; MIT, room 2-338

		Andrei Zelevinsky (Northeastern)

		   Quasicommuting families of 
		quantum type Plucker coordinates
 

This is an account of a joint work with Bernard Leclerc.  We consider 
the q-deformation of the coordinate ring of the flag variety of type 
A_r . This is the algebra with unit over the field of rational functions 
Q(q) generated by 2^{r+1}-1 generators [J] labeled by nonempty subsets
J \subset [1,r+1] := {1,2, ..., r+1} , subject to the quantized Pl\"ucker 
relations.  We refer to the generators [J] as _quantum_flag_minors_
(they can be identified with q-minors of a generic q-matrix whose row 
set consists of several initial rows).  We say that [I] and [J] 
_quasicommute_ if [J][I] = q^n [I][J] for some integer n.  We are 
concerned with the following problem motivated by the study of canonical 
bases for quantum groups of type A_r .
 
Problem A: describe all families of quasicommuting quantum flag minors. 
 
We obtain a combinatorial criterion for quasicommutativity of two quantum 
flag minors [I] and [J].  As a consequence, we show that the maximal 
possible size of a quasicommuting family of quantum flag minors is 
{r+2 \choose 2}.  An interesting special class of such families is in a
bijection with the set of commutation classes of reduced expressions 
for the longest permutation w_0 \in S_{r+1}.  This result leads to a 
natural extension of the _second_Bruhat_order_ by Manin-Schechtman.   
 

Date:           Wed, 3 Apr 1996 10:31:30 -0500 (EST)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Fan, 4/12

Friday, April 12, 4:15 p.m.; MIT, room 2-338

		Ken Fan (Harvard)

	Schubert varieties and short braidedness
 

The theorem I will prove is this:  In a finite type Weyl group,
an element w has the property that you can knock out any simple 
generator from any reduced expression and come up with another 
reduced expression if and only if w is sts-avoiding.  I'll use 
this fact to exhibit a family of singular Schubert varieties.

One curious thing is that this fact depends on finite type and 
is not a purely braid relation fact since it isn't true in affine 
A_2, for instance.

Date:           Wed, 3 Apr 1996 11:44:07 -0500 (EST)
From:           Sergey Fomin <fomin(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Baxter, April 8

APPLIED MATHEMATICS COLLOQUIUM
Monday, April 8, 1996, 4:15 p.m.
M.I.T., Building 2, Room 105

Professor Rodney J. Baxter (Australian National University)
will speak on
"The hard hexagon model and Rogers-Ramanujanism"

Refreshments will be served from 3:45 p.m. in Building 2, Room 349.

From propp(at-sign)math.mit.edu Tue Apr  9 18:09:38 1996
To: combinatorics(at-sign)math.mit.edu
Subject: new URL for archive

The archive is now

http://www-math.mit.edu/~propp/combinatorics-archive/

Jim

Date:           Wed, 10 Apr 1996 13:33:15 -0400
To:             kcollins(at-sign)mail.wesleyan.edu
From:           kcollins(at-sign)wesleyan.edu (Karen L. Collins)

               Come to the TWENTIETH one day conference on

                     Combinatorics and Graph Theory

                      Saturday, April 27, 1996

                         10 a.m. to 4:30 p.m.
                                  at
                            Smith College
                         Northampton MA 01063

                               Schedule

10:00  Vera Pless (University of Illinois at Chicago)
        TBA

11:10  Problem Session by Participants
        Send in contributions by Thursday, April 25th

12:30  Pizza Lunch!!

 2:00  Brenda Latka (DIMACS)
        Forbidden Subtournaments and Antichains

 3:10  Linda Lesniak (Drew University)
        Tough Graph Theory

*Our three year NSF grant is ending this spring.  Looking at the
remaining budget, we have to reduce the transportation allowance
for non-local participants for the April 27th conference to $40
(from the usual $50).  We have applied for a renewal for another
3 years of grant support, and hope to hear soon from NSF.*

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

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, 10 Apr 1996 13:33:59 -0400
To:             kcollins(at-sign)mail.wesleyan.edu
From:           kcollins(at-sign)wesleyan.edu (Karen L. Collins)

PROBLEM SESSION

at the

CoNE meeting Saturday, April 27.

Please submit problems (keep to one page please) in TeX, ASCII, or hard
copy on or before April 25.  Early submissions will be appreciated.

Send to Mike Albertson (Math Dept., Smith College, Northampton, MA 01063) or
Albertson(at-sign)smith.smith.edu

Date:           Tue, 16 Apr 1996 18:33:03 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        RotaFest schedule (LaTeX source)

% LaTeX file of Rotafest Program
\documentclass[12pt]{article} 
\usepackage{amssymb,latexsym}
\baselineskip0.20truein
\parskip0.20truein
\pagestyle{empty}

\begin{document}

\begin{center}
{\bf\Large ROTAFEST PROGRAM}\\[.5in]
{\bf Tuesday, April 16}\\[.2in]
\end{center}
\begin{tabbing}
aaa\=aaaaaaaaaaaaaaaaaa\=\kill
\>7:00--9:30 p.m.\> reception at Charles Hotel\\
\end{tabbing}

\begin{center}
{\bf Wednesday, April 17}\\[.2in]
\end{center}
\begin{tabbing}
aaa\=aaaaaaaaaaaaaaaaaa\=\kill
\>9:00--12:00\> morning session, room 9-150 (Andr\a'e Joyal, chair)\\
\>9:00--9:30\> Adriano Garsia, The $n!$-conjecture and the $q,t$
Kostka polynomials \\
\>9:45--10:15\> Stephen Grossberg, Nonlinear dynamics of neural networks\\
\>10:45--11:15\> Mark Haiman\\
\>11:30--12:00\> Lawrence Harper, The peaks of partition numbers\\[.2in]
\>2:00--5:00\> afternoon session (Erwin Lutwak, chair)\\
\>2:00--2:30 \> Jay Goldman, Combinatorics and knot theory\\
\>2:45--3:15\> Daniel Klain, Invariant valuations on convex bodies\\
\>3:45--4:15\> Joseph Kung, Line sizes and the number of points
in a matroid\\
\>4:30--5:00\> Andrew Odlyzko\\
\end{tabbing}

\begin{center}
{\bf Thursday, April 18}\\[.2in]
\end{center}

\begin{tabbing}
aaa\=aaaaaaaaaaaaaaaaaa\=\kill
\>9:00--12:00 \> morning session (Steve Tanny, chair)\\
\>9:00--9:30 \> Willaim Schmitt\\
\>9:45--10:15\> Bruce Sagan, Beyond semimodular lattices\\
\>10:45--11:15\> Pat O'Neil\\
\>11:30--12:00\> David Sharp, Raleigh-Taylor instability, chaotic
mixing layer\\
\>\> \quad\quad and stochastic PDE's\\[.2in]
\>2:00--5:00\> afternoon session (Peter Doubilet, chair)\\
\>2:00--2:30\> Richard Stanley, Hyperplane arrangements, inversions,
and trees\\
\>2:45--3:15\> Joel Stein, The future of invariant theory\\
\>3:45--4:15\> Bernd Sturmfels, Lattice walks and primary decomposition\\
\>4:30--5:00\> Neil White, Coxeter matroids\\[.2 in]
\>6:00--10:00\> banquet, Hyatt Regency Hotel\\
\end{tabbing}

\begin{center}
{\bf Friday, April 19}\\[.2in]
\end{center}

\begin{tabbing}
aaa\=aaaaaaaaaaaaaaaaaa\=\kill
\> 9:00--12:00 \> morning session (Joseph Oliviera, chair)\\
\>9:00--9:30 \> Walter Whiteley, Two matroids from geometric
homology:\\
\>\> \quad\quad an analogy with digressions\\
\>9:45--10:15\> Kenneth Baclawski, Politically correct ordered sets:\\
\>\> \quad\quad Socially responsible combinatorics\\
\>10:45--11:15\> Wendy Chan, Classification of trivectors in 6-D space\\
\>11:30--12:00\> David Buchsbaum, Letter-place methods and homotopy\\[.2in]
\>\> afternoon free\\[.2in]
\> 6:30 \> dinner at Salamander\\
\> around 6:30 \> alternate dinner at Royal East\\
\end{tabbing}

\begin{center}
{\bf Saturday, April 20}\\[.2in]
\end{center}

\begin{tabbing}
aaa\=aaaaaaaaaaaaaaaaaa\=\kill
\>9:00--12:00 \> morning session (Curtis Greene, chair)\\
\>9:00--9:30 \> Henry Crapo, Unities and negation:\\
\>\> \quad\quad On the representation of lattices\\
\>9:45--10:15\> {\bf Gian-Carlo Rota}, Ten lessons I should have been
taught\\ 
\>10:45--11:15\> Peter Duren\\
\>11:30--12:00\> Richard Ehrenborg, Coproducts and the $cd$-index\\[.2in]
\>2:00--5:00\> afternoon session (Michael Hawrylycz, chair)\\
\>2:00--2:30\> Steven Fisk\\
\>2:45--3:15\> Jack Freeman\\
%\>3:45--4:15\>
%\>4:30--5:00\>
\end{tabbing}
\end{document}

Date:           Wed, 17 Apr 1996 01:31:18 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Tesler, 4/24

Wednesday, April 24, 4:15 p.m.; MIT, room 2-338

		  Glenn Tesler (U.C. San Diego)

		   Plethystic formulas for the
		Macdonald q,t-Kostka coefficients

Macdonald introduced a two parameter symmetric function basis
P_\mu(x;q,t) for which various specializations of q and t yield
many of the other well-established bases.  The transition matrix
expressing a rescaled basis J_\mu(x;q,t) in terms of a modified
Schur basis s_\lambda[X(1-t)] has components denoted 
K_{\lambda,\mu}(q,t), and generalizes the ordinary Kostka matrix.
Macdonald conjectured that K_{\lambda,mu}(q,t) are polynomials in
q and t with nonnegative integer coefficients.  We show that they
are polynomials by determining new explicit formulas for them.  
These formulas separate the dependence on \mu and \lambda, and
surprisingly, their structure is entirely determined by a portion of
\lambda, and not at all on \mu.  These formulas are themselves
symmetric functions k_\gamma(x;q,t) indexed by partitions, where if
we set \gamma to be \lambda with its largest row deleted, then a
certain specialization ``B_\mu'' of x to q,t-monomials depending on
\mu essentially expresses K_{\lambda,\mu}(q,t) as k_\gamma(B_\mu;q,t).  
The coefficients of k_gamma(x;q,t) when expressed in terms of 
Schur functions are Laurent polynomials in q and t, so that 
k_\gamma(B_\mu;q,t) is at least a Laurent polynomial, and the simple 
monomial denominator is easily eliminated to yield a true polynomial.

This is joint work with Adriano Garsia.

Date:           Thu, 18 Apr 1996 07:54:50 -0400
To:             kcollins(at-sign)mail.wesleyan.edu
From:           kcollins(at-sign)wesleyan.edu (Karen L. Collins)
Subject:        after taxes

OK, now that your taxes are done, how about sending a problem for the
problem session to Mike Albertson (albertson(at-sign)smith.smith.edu).  See you
April 27.

Date:           Thu, 18 Apr 1996 07:56:49 -0400
To:             kcollins(at-sign)mail.wesleyan.edu
From:           kcollins(at-sign)wesleyan.edu (Karen L. Collins)

               Come to the TWENTIETH one day conference on

                     Combinatorics and Graph Theory

                      Saturday, April 27, 1996

                         10 a.m. to 4:30 p.m.
                                  at
                            Smith College
                         Northampton MA 01063

                               Schedule

10:00  Vera Pless (University of Illinois at Chicago)
        Constraints on Weight in Binary Codes

11:10  Problem Session by Participants
        Send in contributions by Thursday, April 25th

12:30  Pizza Lunch!!

 2:00  Brenda Latka (DIMACS)
        Forbidden Subtournaments and Antichains

 3:10  Linda Lesniak (Drew University)
        Tough Graph Theory

*Our three year NSF grant is ending this spring.  Looking at the
remaining budget, we have to reduce the transportation allowance
for non-local participants for the April 27th conference to $40
(from the usual $50).  We have applied for a renewal for another
3 years of grant support, and hope to hear soon from NSF.*

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

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:           Fri, 19 Apr 1996 15:58:45 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Robins, 4/26

Friday, April 26, 4:15 p.m.; MIT, room 2-338

		Sinai Robins (U.C. San Diego)

	The Ehrhart Polynomial of a Lattice Polytope

The problem of counting the number of lattice points inside a 
lattice polytope in R^n has been studied from a variety of 
perspectives, including the recent work of Pommersheim and 
Kohvanskii using toric varieties and Cappell and Shaneson using 
Grothendieck-Riemann-Roch.  Here we show that the Ehrhart 
polynomial of a lattice n-simplex has a simple analytical 
interpretation from the perspective of function theory on the
n-torus. The methods involve Poisson Summation and Fourier 
integrals.

We obtain closed forms for the coefficients of the Ehrhart 
polynomial in terms of the elementary cotangent functions.  
These expressions are closely related to the formulas of 
Cappell and Shaneson and Hirzebruch and Zagier.

This is joint work with Ricardo Diaz.

Date:           Tue, 23 Apr 1996 11:06:36 -0400
To:             kcollins(at-sign)mail.wesleyan.edu
From:           kcollins(at-sign)wesleyan.edu (Karen L. Collins)
Subject:        problem session

This is a final reminder.  Please send problems for the April 27th meeting
to Mike Albertson (albertson(at-sign)smith.smith.edu)

Date:           Wed, 24 Apr 1996 11:47:54 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        MIT Combinatorics Seminar: May schedule

Here is a list of talks currently scheduled for the month of May.
Notice that all talks will begin at 4:15 p.m.

Wednesday, May 1, 4:15 p.m.: Yuval Roichman,
	A recursive rule for Kazhdan-Lusztig characters

Wednesday, May 8, 4:15 p.m.: Sergey Fomin,
	Quantum Schubert polynomials
	[followed by Discrete Dinner at 6 p.m.]

Friday, May 17, 4:15 p.m.: Frank Sottile,
	Symmetries of Littlewood-Richardson coefficients for 
	Schubert polynomials

Wednesday, May 22, 4:15 p.m.: Rodney Baxter,
	Star-triangle and star-star relations in statistical mechanics

All talks will meet in room 2-338.

Date:           Wed, 24 Apr 1996 11:48:54 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Roichman, 5/1

Wednesday, May 1, 4:15 p.m.; MIT, room 2-338

		    Yuval Roichman (M.I.T.)

	A recursive rule for Kazhdan-Lusztig characters
 

The Murnaghan-Nakayama rule is a most useful recursive rule
for computing characters of the symmetric groups.  We present 
a generalization of this rule to arbitrary Coxeter groups and 
their Hecke algebras.  The classical version is obtained as a 
special case, and  new combinatorial interpretations follow. 
The work is done via Kazhdan-Lusztig theory and combinatorics 
of Coxeter groups.

Date:           Wed, 24 Apr 1996 16:15:25 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        MIT Combinatorics Seminar: May schedule (REVISED)

Here is a revised list of talks currently scheduled for the month of May.
Notice that a new talk has been added on May 15.

Wednesday, May 1, 4:15 p.m.: Yuval Roichman,
	A recursive rule for Kazhdan-Lusztig characters

Wednesday, May 8, 4:15 p.m.: Sergey Fomin,
	Quantum Schubert polynomials
	[followed by Discrete Dinner at 6 p.m.]

Wednesday, May 15, 4:15 p.m.: Sara Billey,
	Vexillary elements in the hyperoctahedral group

Friday, May 17, 4:15 p.m.: Frank Sottile,
	Symmetries of Littlewood-Richardson coefficients for 
	Schubert polynomials

Wednesday, May 22, 4:15 p.m.: Rodney Baxter,
	Star-triangle and star-star relations in statistical mechanics

All talks will meet in room 2-338.

Date:           Fri, 26 Apr 1996 00:19:39 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Discrete Dinner

		        Spring 1996 Boston Area 
		      Discrete Mathematics Dinner
		         (second announcement)

This semester's Discrete Dinner will be held on Wednesday, May 8
at 6 p.m. at Helmand's Restaurant (143 First Street, Cambridge)
between Kendall Square and Lechmere.  The cost will be $10 for 
grad students and undergraduates (alcoholic beverages not included), 
with the rest of us making up the difference.  

Please let me know by May 1 (preferably electronically) your 
probability of attendance (if you haven't already done so).  
My e-mail address is propp(at-sign)math.mit.edu; if you don't have 
e-mail, call 253-6544.

Date:           Wed, 1 May 1996 12:58:24 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Fomin, 5/8

Wednesday, May 8, 4:15 p.m.; MIT, room 2-338

		    Sergey Fomin (M.I.T.)

		Quantum Schubert polynomials

We compute the Gromov-Witten invariants of the flag manifold using a 
new combinatorial construction for its quantum cohomology ring.

This is joint work with S. Gelfand and A. Postnikov.  The paper is 
available from http://www-math.mit.edu/~fomin/papers.html

Date:           Wed, 8 May 1996 22:38:07 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Billey, 5/15

Wednesday, May 15, 4:15 p.m.; MIT, room 2-338

		     Sara Billey (M.I.T.)

	Vexillary elements in the hyperoctahedral group
 

The vexillary permutations in the symmetric group have interesting
connections with the number of reduced words, the Littlewood-Richardson 
rule, Stanley symmetric functions, Schubert polynomials and the Schubert 
calculus.  Lascoux and Schutzenberger have shown that vexillary permutations 
are characterized by the property that they avoid any subsequence of length 
4 with the same relative order as 2143.  In this talk, we will propose a 
definition for vexillary elements in the hyperoctahedral group.  We show 
that the vexillary elements can again be determined by pattern avoidance
conditions.  These vexillary elements share some, but not all, of the
"nice" properties of the vexillary permutations in $S_n$.

Date:           Fri, 10 May 1996 14:18:25 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Sottile, 5/17

Friday, May 17, 4:15 p.m.; MIT, room 2-338

	       Frank Sottile (Toronto)

	 Symmetries of Littlewood-Richardson 
	coefficients for Schubert polynomials

The Littlewood-Richardson rule is a combinatorial formula for 
structure constants of the ring of symmetric polynomials 
in terms of its Schur basis:

s_\mu \cdot s_\nu = \sum_\lambda c^\lambda_{\mu\,\nu} s_\lambda.

Schubert polynomials form a basis for the ring of polynomials in 
infinitely many variables x_1,x_2,..., so there are similar 
structure constants for Schubert polynomials, which I also call  
Littlewood-Richardson coefficients.  These generalize the classical 
coefficients, as every Schur polynomial in  x_1,...,x_k  is a 
Schubert polynomial.  They are, however, largely unknown.

This talk will discuss recent results (obtained with Nantel Bergeron) 
on those coefficients which arise when multiplying a Schubert polynomial 
by a Schur polynomial.  We show these coefficients have certain 
symmetries, similar to symmetries of the classical Littlewood-Richardson 
coefficients, which facilitates their computation.  We apply these 
results to the enumeration of chains in the strong Bruhat order on the 
symmetric group.

Date:           Mon, 13 May 1996 23:11:50 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Billey, 5/15; CHANGE OF TIME

Sara Billey's MIT Combinatorics Seminar talk, entitled "Vexillary elements 
in the hyperoctahedral group", will take place this coming Wednesday (May 15) 
beginning at 5 p.m., rather than 4:15 as originally planned.  Sorry for any 
inconvenience.  Please spread the word if possible.

Jim Propp

Date:           Wed, 15 May 1996 09:22:20 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Baxter, 5/22

Wednesday, May 22, 4:15 p.m.; MIT, room 2-338

		Rodney Baxter (Australian National University 
			and Northeastern University)

	Star-triangle and star-star relations in statistical mechanics
 

The star-triangle is the simplest form of the ``Yang-Baxter'' relations 
and plays a vital role in solvable statistical mechanical models, 
ensuring that transfer matrices commute.

There are models for which no star-triangle relation is known, but
which satisfy a weaker ``star-star'' relation. These will be discussed,
and it will be shown that this weaker relation is still sufficient to
ensure the required commutation properties.

Date:           Sun, 19 May 1996 14:42:21 -0400 (EDT)
From:           Jim Propp <propp(at-sign)math.mit.edu>
To:             combinatorics(at-sign)math.mit.edu
Subject:        Shimozono, 5/24

Friday, May 24, 4:15 p.m.; MIT, room 2-338

		Mark Shimozono (M.I.T.)

	Monotonicity properties of q-analogues of 
	   Littlewood-Richardson coefficients
 

Certain q-analogues of Littlewood-Richardson (LR) coefficients arise
naturally in the resolution of the ideal of a nilpotent conjugacy classes of
matrices in a larger nilpotent conjugacy class.  These polynomials may be
defined using a Kostant-Heckman formula.  A conjectural description 
is given in terms of what we call catabolizable tableaux.  In the special
case of tensor products of irreducibles corresponding to rectangular
partitions, there is another conjectural combinatorial description using
classical LR tableaux and a generalization of Lascoux, Leclerc, and Thibon's
formula for the charge statistic.  Monotonicity properties of these
polynomials are studied using families of statistic-preserving injections.
Certain compositions of these injections furnish a bijection from the LR
tableaux to the catabolizables.  This is joint work, part with Jerzy Weyman
and part with Anatol N. Kirillov.