Math Calendar
Tuesday, May 12, 2026
16:00-17:00
HFG 7.07
A (proper) $k$-coloring of a graph $G$ is a function assigning a \say{color} chosen from $\{1,2, \dots, k\}$ to each of the vertices of the graph with the property that no two adjacent vertices receive the same color.
The chromatic number $\chi(G)$ is the minimum $k$ for which there exists a $k$-coloring of $G$.
Testing $k$-colorability is a classic NP-Hard problem and graph coloring lies at the center of modern graph theory.
The \say{dual parameter} to the chromatic number is the clique number $\omega$.
A \emph{clique} is a set of pairwise adjacent vertices in a graph.
It's easy to see that all vertices in a clique must all receive different colors in any proper coloring.
The \emph{clique number} $\omega(G)$ is the maximum size of a clique in $G$.
Trivially, $\chi(G) \geq \omega(G)$.
Unfortunately, we cannot in general obtain any upper bound on the chromatic number in terms of the clique number.
There are classical constructions for graphs of triangle-free graphs with arbitrarily large chromatic number.
Moreover, it is s a well-known result of Erd\H{o}s that for every $g \geq 3$ there exist graphs with arbitrarily large chromatic number and with no cycle of length less than $g$.
Inspired by perfect graphs, the area of \chi-boundedness seeks to understand what structural conditions admit such a bound.
This talk will introduce the general area of \chi-boundedness and will survey some of the speakers work in the area.
No prior knowledge of graph theory will be assumed.
The chromatic number $\chi(G)$ is the minimum $k$ for which there exists a $k$-coloring of $G$.
Testing $k$-colorability is a classic NP-Hard problem and graph coloring lies at the center of modern graph theory.
The \say{dual parameter} to the chromatic number is the clique number $\omega$.
A \emph{clique} is a set of pairwise adjacent vertices in a graph.
It's easy to see that all vertices in a clique must all receive different colors in any proper coloring.
The \emph{clique number} $\omega(G)$ is the maximum size of a clique in $G$.
Trivially, $\chi(G) \geq \omega(G)$.
Unfortunately, we cannot in general obtain any upper bound on the chromatic number in terms of the clique number.
There are classical constructions for graphs of triangle-free graphs with arbitrarily large chromatic number.
Moreover, it is s a well-known result of Erd\H{o}s that for every $g \geq 3$ there exist graphs with arbitrarily large chromatic number and with no cycle of length less than $g$.
Inspired by perfect graphs, the area of \chi-boundedness seeks to understand what structural conditions admit such a bound.
This talk will introduce the general area of \chi-boundedness and will survey some of the speakers work in the area.
No prior knowledge of graph theory will be assumed.
Thursday, May 14, 2026
13:00-14:30
HFG 7.07
Wallcrossing Techniques in Algebraic Geometry seminar
Virtual Classes of Hilbert Schemes of Points, Tomás
see description
Further details and meeting link: https://www.uu.nl/staff/TManopulo/Extra2
17:30-21:30
HFG Library
Monday, May 18, 2026
Tuesday, May 19, 2026
Thursday, May 21, 2026
17:30-21:30
HFG Library
Friday, May 22, 2026
10:00-12:30
Ruppert-Rood
Dutch Differential Topology and Geometry seminar
Klaus Niederkruger - Fillability of Legendrians by exact Lagrangians
see description
Contact topology is often referred to as the odd-dimensional counterpart of symplectic topology. The most natural link between the two is considering contact manifolds as the boundaries of symplectic manifolds. In this context, one might wonder whether a given contact manifold is the boundary of a symplectic manifold and, if so, what information about the symplectic manifold can be extracted from the contact manifold.
Currently, most questions of this type are studied using sophisticated Floer homologies. In the first part of my presentation, I will explain the initial methods from the '80s that were much more geometric. I want to sketch how to prove two classical results: the standard contact sphere can only bound a symplectic ball and an overtwisted contact structure cannot bound any symplectic manifold.
In the second half of my presentation, I will discuss submanifolds. The most interesting submanifold of a symplectic manifold is a Lagrangian; the most interesting submanifold of a contact manifold is a Legendrian. One can then study whether a Legendrian lying in a contact boundary of a symplectic manifold is itself a boundary of a Lagrangian. Many results are known, but they also rely on advanced Floer homology. In the joint work with Casim Abbas that I want to talk about, we generalize the initial geometric proofs to reproduce the classical Legendrian analogues of the statements above.
Website of the seminar: https://www.few.vu.nl/~trt800/ddtg.html
Currently, most questions of this type are studied using sophisticated Floer homologies. In the first part of my presentation, I will explain the initial methods from the '80s that were much more geometric. I want to sketch how to prove two classical results: the standard contact sphere can only bound a symplectic ball and an overtwisted contact structure cannot bound any symplectic manifold.
In the second half of my presentation, I will discuss submanifolds. The most interesting submanifold of a symplectic manifold is a Lagrangian; the most interesting submanifold of a contact manifold is a Legendrian. One can then study whether a Legendrian lying in a contact boundary of a symplectic manifold is itself a boundary of a Lagrangian. Many results are known, but they also rely on advanced Floer homology. In the joint work with Casim Abbas that I want to talk about, we generalize the initial geometric proofs to reproduce the classical Legendrian analogues of the statements above.
Website of the seminar: https://www.few.vu.nl/~trt800/ddtg.html
Monday, May 25, 2026
Tuesday, May 26, 2026
Thursday, May 28, 2026
13:00-14:30
HFG 7.07
Further details and meeting link: https://www.uu.nl/staff/TManopulo/Extra2
17:30-21:30
HFG Library
Friday, May 29, 2026
Tuesday, June 2, 2026
Thursday, June 4, 2026
13:00-14:00
HFG611
17:30-21:30
HFG Library
Friday, June 5, 2026
Monday, June 8, 2026
Tuesday, June 9, 2026
Thursday, June 11, 2026
13:00-14:30
HFG 7.07
Wallcrossing Techniques in Algebraic Geometry seminar
The Vertex Algebra in equivariant geometry, Arkadij
see description
Further details and meeting link: https://www.uu.nl/staff/TManopulo/Extra2
17:30-21:30
HFG Library
Monday, June 15, 2026
Tuesday, June 16, 2026
Thursday, June 18, 2026
13:00-14:00
13:00-14:30
HFG 7.07
Further details and meeting link: https://www.uu.nl/staff/TManopulo/Extra2
17:30-21:30
HFG Library
Friday, June 19, 2026
Monday, June 22, 2026
Tuesday, June 23, 2026
Thursday, June 25, 2026
17:30-21:30
HFG Library
Tuesday, June 30, 2026
Thursday, July 2, 2026
17:30-21:30
HFG Library
Tuesday, July 7, 2026
Thursday, July 9, 2026
17:30-21:30
HFG Library
Thursday, July 16, 2026
17:30-21:30
HFG Library
Thursday, July 23, 2026
17:30-21:30
HFG Library
Thursday, July 30, 2026
17:30-21:30
HFG Library
Thursday, August 6, 2026
17:30-21:30
HFG Library
Thursday, August 13, 2026
17:30-21:30
HFG Library
Thursday, August 20, 2026
17:30-21:30
HFG Library
Thursday, August 27, 2026
17:30-21:30
HFG Library
Thursday, September 3, 2026
17:30-21:30
HFG Library
Thursday, September 10, 2026
17:30-21:30
HFG Library
Thursday, September 17, 2026
17:30-21:30
HFG Library
Thursday, September 24, 2026
17:30-21:30
HFG Library
Thursday, October 1, 2026
17:30-21:30
HFG Library
Thursday, October 8, 2026
17:30-21:30
HFG Library
Thursday, October 15, 2026
17:30-21:30
HFG Library
Thursday, October 22, 2026
17:30-21:30
HFG Library
Thursday, October 29, 2026
17:30-21:30
HFG Library
Thursday, November 5, 2026