K O I   C O M B I N A T O R I C S   L E C T U R E S

The KOI Combinatorics Lectures is a joint venture between combinatorialists from the Kentucky, Ohio and Indiana area.

The goal of this series of meetings is to foster and build intergenerational friendship and collaboration between researchers broadly defined (graduate students, postdocs, faculty) in the KOI area.

Organizing Committee:
Saúl A. Blanco (IU), Mihai Ciucu (IU), Richard Ehrenborg (UK), Eric Katz (OSU), Margaret Readdy (UK)

F A L L   2 0 2 4

Third meeting: October 4 and 5, 2024 (in-person)

Location: Indiana University, Bloomington IN

Local Organizing Committee:
Sanjana Agarwal (IU), Saúl A. Blanco (IU), Mihai Ciucu (IU), Clay Collier (IU), Jill Clancy (IU, Caleb Schultz Kisby (IU), Ping Lin (IU), Laura Reed (IU).
 

Speakers: Anna Weigandt (University of Minnesota), Bridget Tenner (DePaul University), Seok Hyun Byun (Clemson University).

There will also be a Colloquium talk on Friday, October 4th by Sergey Fomin (University of  Michigan).

Conference Schedule:

Friday, October 4, 2024
03:14 (π time) - 03:50 pm Tea
04:10 - 05:10 pm Sergey Fomin, Seymour Sherman Memorial Lecture,  Incidence geometry and tiled surfaces
06:00 - 08:00 pm Colloquium Dinner

The Colloquium tea will be held in the Cora B. Hennel Lounge (Rawles Hall  107).
The Colloquium talk will be held in Swain East 105 (SE 105). 

Saturday, October 5, 2024
09:00 - 10:00 am  Arrival/Registration/Meet and Greet
09:59 - 10:00 am  Welcome, Welcome speech
10:00 - 11:00 am  Anna Weigandt, Weak order on alternating sign matrix varieties
11:00 - 11:30 am  Coffee Break
11:30 - 12:30 pm  Seok Hyun Byun, Squarish graphs, Aztec triangles, and related dimer bijections
12:30 - 02:30 pm  Lunch Break
02:30 - 03:14 pm  Problem Session
03:14 (π time) - 04:00 pm  Tea time and the One Picture/One Theorem Poster Session
04:00 - 05:00 pm  Bridget Tenner, New impacts of permutation patterns
05:01 - 05:10 pm  Conference Photo
06:00 - 08:00 pm  Conference Dinner

The Saturday talks and problem session will be held at Luddy Hall 1106, Dorsey Auditorium.
The poster session, coffee breaks and tea time will be held in the Luddy Hall Atrium.

Talk Titles and Abstracts:

Seok Hyun Byun, "Squarish graphs, Aztec triangles, and related dimer bijections"

We present two perfect matching (dimer) bijections and show their applications. First, we introduce a large class of symmetric graphs and show that the numbers of their perfect matchings are given by squares of integers or two times them (we call such numbers “squarish”). Secondly, we answer a question posed by Corteel, Huang, and Krattenthaler on finding an explicit bijection between domino tilings of two similar regions called (generalized) Aztec triangles. If time permits, we also introduce a new combinatorial object that is equinumerous to the domino tilings of Aztec triangles. This talk is based on a joint work with Mihai Ciucu.  https://arxiv.org/pdf/2508.04545, https://arxiv.org/abs/2404.09930 

Sergey Fomin, "Incidence geometry and tiled surfaces"

We show that various classical theorems of linear incidence geometry, such as the theorems of Pappus, Desargues, Möbius, and so on, can be interpreted as special cases of a general result that involves a triangulation of a closed oriented surface, or a tiling of such a surface by quadrilateral tiles. This yields a general mechanism for producing new incidence theorems and generalizing the known ones.  This is joint work with Pavlo Pylyavskyy.   https://arxiv.org/abs/2305.07728  slides 

Bridget Tenner, "New impacts of permutation patterns"

Permutations are a classic tool for representing mathematical scenarios. The study of permutations in their own right, as combinatorial objects, has blossomed in the last half century through a burgeoning interest in permutation patterns. This leads naturally to an abundance of enumerative questions, but the patterns that a given permutation contains (or avoids) have also shown substantial relevance -- and with applications to numerous other fields. We will discuss several major themes of that research, as well as exciting and relatively new directions for the field. These directions, sometimes complementary to some of the classical results, have already shown great utility and are poised for even more.  This is joint work with Yosef Berman and with Joel Lewis.  https://arxiv.org/pdf/2110.11146, https://arxiv.org/abs/2504.13108 

Anna Weigandt, "Weak order on alternating sign matrix varieties" 

Alternating sign matrices (ASMs) form the MacNeille completion of the strong Bruhat order on the symmetric group.  There is a natural interpretation of this poset as the containment order on ASM varieties, which are generalized determinantal ideals.  In 2018, Hamaker and Reiner defined weak Bruhat order on ASMs, which when restricted to the symmetric group, is the usual weak order.  We initiate a geometric study of weak order on ASMs varieties, focusing on how combinatorial properties of this poset describe geometric properties of ASM varieties.  This is joint work with Laura Escobar and Patricia Klein.  slides

One Picture One Theorem Poster Session Presenters:

Suman Balasubramanian, "TBA"

Csaba Biro, "Independent cliques in a partially apexiated octahedron"

Saúl Blanco, "Some integer eigenvalues of prefix-reversal graphs"

Judy Hsin-Hui Chiang, "Combinatorial models of Schubert and Grothendieck polynomials"

Richard Ehrenborg, "A Speicher theorem for the d-indivisible noncrossing partition posets"

Aditya Guha Roy, "How many mazes can we escape using the same path?"

Yi-Lin Lee, "Counting k-sorted labelings of a poset"

Yichen Ma, "Supersolvable convex geometries"

Brian Macdonald, "An Alternate Proof for the Top-Heavy Conjecture on Partition Lattices Using Shellability"

Jaewon Min, "Saturation of Littlewood-Richardson coefficients and Newell-Littlewood numbers"

Chloe' Napier, "Extensions in the preprojective algebras"

Williem Rizer, "Positroid flags are Bruhat intervals"

Registration is closed:  Registration form (closes September 21)  Due to the caterer deadline, those who register after September 21, 2024 will unfortunately not be able to be included at the conference dinner.

Location:  The Friday Colloquium tea will be held at Rawles Hall 107, 831 E Third Street.  The Colloquium talk will be held Swain Hall East, 729 E Third Street.  All Saturday conference activities (talks, problem session, poster session and conference dinner) will be held at Luddy Hall, 700 N Woodlawn Avenue.

Parking:  For Friday, parking near Rawles for the colloquium:  Henderson Parking Garage, 310 S Fess Avenue, Bloomington IN 47401 (located on Fess Avenue between Atwater and Third Street) and the Atwater Parking Garage, 921 E Atwater Avenue, Blomingtno IN 47401 (located on faculty Drive between  Third Street and Atwater Ave).

For Saturday, parking is available across the street at Luddy AI Center, 1015 E 11th Street, Bloomington IN 47408.  Note that while this parking is metered, the exit gates are open during the weekend. 

Hotels:  We have reserved a block of rooms at the Indiana Memorial Union Biddle Hotel and Conference Center.  The group rate is $138.60 (single), $174.60 (double) + tax per room per night.  The Hotel Group Code is:  KOI24.  The Biddle Hotel Guest Parking Fee is $6 per car per day to be added to the hotel account. To make reservations: 800-209-8145 or 812-856-6381 or www.imu.indiana.edu.  The last day to make reservations is September 3, 2024.  

Other options include the Hyatt Place Bloomington on Kirkwood Avenue and the Hilton Garden Inn on North College Avenue.  Each is about an 18 minute walk to the IU Math Dept.

Funding:  It's official!!!  The NSF DMS is funding our conference grant for the KOI Combinatorics Lectures.  This will provide partial funding for participant travel and local costs.  Priority will be placed on funding those individuals to participate who do not have access to other federal support, or who are students, post-doctoral scholars, or from underrepresented groups.  

Funding request form:  link (due September 2, 2024)

Childcare and family care conference resources:  In order to encourage participants whose attendance is contingent in having childcare or family care in place, the NSF has generously provided childcare and family care support.  Please indicate any need when you register.

There are a number of campus and community resources to support childcare and family care needs at Indiana University and in Bloomington, Indiana during the Fall 2024 KOI Combinatorics Lectures.  Please see:  Child Care resources -- Office of the Vice Provost for Faculty & Academic Affairs  

Lunch:  Here is a lunch map prepared by Yi-Lin Lee.  It also includes the colloquium and conference location, as well as Biddle Hotel area:  

Pre-registered Participants (so far):

Sanjana Agrawal (Indiana U)

Suman Balasubramanian (DePauw U)

Allan Bickle (Purdue)

Bethany Baker (U Kentucky)

Csaba Biro (U Louisville)

Saúl A. Blanco (Indiana U)

Eric Burkholder (U Kentucky)

Seok Hyun Byun (Clemson U)

Pablo Castilla (U Kentucky)

Ian Cavey (UIUC)

Judy Chiang (U Minnesota)

Mihai Ciucu (Indiana U)

Alvaro Cornejo (U Kentucky)

Cesar Cuenca (The Ohio State U)

Soren DeHaan (Indiana U)

Hugh Dennin (The Ohio State U)

Aiden Dunkelberg (Indiana U)

Richard Ehrenborg (U Kentucky)

Laura Escobar (Washington U St. Louis)

Sergey Fomin (U Michigan)

David Galvin (Notre Dame)

Aditya Guha Roy (Indiana U)

Eric Katz (The Ohio State U)

Omid Khormali (U Evansville)

Nadav Kohen (Indiana U)

Yi-Lin Lee (Indiana U)

Yonglin Lee (UIUC)

Haggai Liu (Simon Fraser U)

Yichen Ma (Cornell)

Brian Macdonald (U Kentucky)

Nishad Mandlik (Indiana U)

Nick Mayers (NC State U)

Brodie McCuen (Indiana U)

Jaewon Min (UIUC)

Sina Nadi (Purdue)

Chloe` Napier (U Kentucky)

Antwon Park (U Kentucky)

Rodrigo Pérez (IU Indianapolis)

Freyja Ragnarsson (ETHS)

Patrek Ragnarsson (ETHS)

Doel Rivera Laboy (U Kentucky)

Aditya Guha Roy (Indiana U)

Margaret Readdy (U Kentucky)

Williem Rizer (U Kentucky)

Caleb Schultz Kisby (Indiana U)

Bridget Tenner (DePaul U)

Kumar Vinayak (U Kentucky)

Anna Weigandt (U Minnesota)

Non-discrimination statement and conduct:  The KOI Combinatorics Lectures promotes and encourages a welcoming environment for individuals from all backgrounds.  We actively promote participation from all career stages and from all backgrounds.

Our goal is to foster a wonderful learning community and exchange of ideas.  As per Federal regulations, there is a zero-tolerance policy for discrimination on the basis of race, ethnicity, color, religion, age, national origin, veteran or service status, disability, any other protected category, or identity. We expect all participants to conduct themselves conscientiously and respectfully. We will not allow harassment or inappropriate behavior. Conference organizers have full discretion to enforce this policy.

The KOI Participant Code of Conduct:   pdf 

If you wish to be added to the KOI Combinatorics Lectures mailing list, please send an e-mail to: koi.combinatorics@gmail.com. 

Last updated:  August 6, 2025