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Friday, May 15, 2026 10:30 am - 11:30 am EDT (GMT -04:00)

Crypto Reading Group - Seunghoon Lee & Bruno Sterner-Introduction to Coding Theory (Part 1)

Speaker:

 Seunghoon Lee & Bruno Sterner
Affiliation: University of Waterloo
Location: MC 5417

Abstract:

For this term's reading group, we will be hosting a study group on code-based cryptography with a focus on understanding HQC — the most recent NIST standard for post-quantum KEM/PKE. We will spend 7 weeks going over the necessary material to cover this topic before concluding with state-of-the-art HQC. A week-by-week plan is outlined at the following link: https://www.leonardocolo.com/seminars/Spring26.html.
For the first week, we will cover the basic definitions and properties of coding theory as well as go over Reed-Solomon codes.
Friday, May 15, 2026 12:30 pm - 1:30 pm EDT (GMT -04:00)

CombOpt ReadingGroup - Kelly Dance-Contract Design Beyond Hidden-Actions

Speaker:

 Kelly Dance
Affiliation: University of Waterloo
Location: MC 6029

Abstract:

In the classical principal-agent hidden-action contract model, a principal delegates the execution of a costly task to an agent. In order to complete the task, the agent chooses an action from a set of actions, where each potential action is associated with a cost and a success probability to accomplish the task. To incentivize the agent to exert effort, the principal can commit to a contract, which is the amount of payment based on the task's success but not on the hidden-action chosen by the agent.
In this work, we study the contract design framework under binary outcomes where we relax the hidden-action assumption. We introduce new models where the principal is allowed to inspect subsets of actions at some cost that depends on the inspected subset. If the principal discovers that the agent did not select the agreed-upon action through the inspection, the principal can withhold payment. This relaxation of the model introduces a broader strategy space for the principal, who now faces a tradeoff between positive incentives (increasing payment) and negative incentives (increasing inspection).
We devise algorithms for finding the best deterministic and randomized incentive-compatible inspection schemes for various assumptions on the inspection cost function. In particular, we show the tractability of the case of submodular inspection cost functions. 
We complement our results by showing that it is impossible to efficiently find the optimal randomized inspection scheme for the more general case of XOS inspection cost functions, and that there is no PTAS for the case of subadditive inspection cost functions."
Friday, May 15, 2026 3:30 pm - 4:30 pm EDT (GMT -04:00)

Tutte Colloquium -Jim Geelen-Tangles in graphs and matroids

Speaker: Jim Geelen
Affiliation: University of Waterloo
Location: MC 5501

Abstract: A common strategy in many proofs and algorithms is to begin by decomposing a graph into more highly connected pieces. Decomposition is easy when the goal is to obtain connected or 2-connected pieces, and decomposition into 3- or 4-connected pieces is also straightforward in many settings. For higher levels of connectivity, however, no effective and widely applicable notion of decomposition is currently known. To address this, Robertson and Seymour introduced tangles, which capture the k-connected regions of a graph without decomposing. 

Thursday, May 21, 2026 2:30 pm - 3:30 pm EDT (GMT -04:00)

Algebraic and Enumerative combinatorics seminar - Kaveh Mousavand-Left modularity and extremality of some (finite and infinite) lattices via representation theory

Speaker: Kaveh Mousavand
Affiliation: Okinawa Institute of Science and Technology
Location: MC 5479

Abstract:Motivated by the representation theory of finite-dimensional algebras, we recently investigated the notions of left modularity and extremality in (completely) semidistributive lattices. For lattices of torsion classes, we obtain a simultaneous characterization of left modularity and extremality in terms of the behavior of certain indecomposable modules, called bricks. Our results extend the classical theory beyond the realm of finite lattices, while remaining within the framework of (completely) semidistributive lattices. Time permitting, I will also discuss extensions of these results to arbitrary infinite lattices that are completely semidistributive and weakly atomic. This talk is based on recent joint work with Sota Asai, Osamu Iyama, and Charles Paquette.

There will be a pre-seminar presenting relevant background at beginning graduate level starting at 1:30pm in MC 5417.

Friday, May 22, 2026 10:30 am - 11:30 am EDT (GMT -04:00)

Crypto Reading Group - Maher Mamah & Elle Wen-Introduction to Code-Based Cryptography (Part 2)

Speaker:

 Maher Mamah & Elle Wen
Affiliation: University of Waterloo
Location: MC 5417

Abstract:

This week, we continue our discussion of codes by introducing the underlying hard problem: the decoding problem, which asks us to decode a random linear code. We also discuss McEliece, one of the oldest code-based public-key encryption schemes, and its instantiations using Goppa codes.
Friday, May 22, 2026 3:30 pm - 4:30 pm EDT (GMT -04:00)

Tutte Colloquium -Sophie Spirkl-Cliques and colouring in tournaments

Speaker: Sophie Spirkl
Affiliation: University of Waterloo
Location: MC 5501

Abstract: A tournament is an orientation of a complete graph, and in terms of structural questions, tournaments are often a natural analogue of graphs. Neumann-Lara, in 1982, defined what it means to colour a tournament. Only recently, in 2023, Aboulker, Aubian, Charbit and Lopes defined what the clique number of a tournament is — but it is a bit more complicated than in graphs. What can we say about these parameters, from a structural and computational point of view? There are a few things to say, including a recent joint result with Logan Crew, Xinyue Fan, Hidde Koerts, and Ben Moore.

[Many of you know the severe consequences that a COVID infection has had for my family. I would consider it a kindness if attendees would wear masks. I will provide free masks for those who may need them.]