This post contains a list of our content from 2020 for easy access. The online talks will resume on **January 11 with a talk by Stephan Kreutzer** from TU Berlin. Thanks to everyone who participated in the open problems session – it was great seeing the problems and seeing you there! Have a good winter break.

**Blog posts:**

- Short rainbow cycles in graphs and matroids
**The geometry of cocircuits and circuits. A tombeau for Henry Crapo 1933 — 2019**- Carmesin’s 3-dimensional version of Whitney’s planarity criterion
- Almost every sparse paving matroid contains M(K4) or W3 as a minor
- The World of Clean Clutters, I: Ideal Clutters
- The rank-3 excluded minors for GF(5)-representability
- The q-analogue of a matroid

**Online talks **[also see the **Youtube playlist]:**

April 16: James Oxley, The binary matroids with no odd circuits of size exceeding five

April 27: Dillon Mayhew, Definability and non-definability for classes of matroids

May 4: Nathan Bowler, Quasi-graphic matroids

May 11: Rudi Pendavingh, Counting valuated matroid types

May 25: Peter Nelson, Extensions and coextensions of cliques

June 1: Iain Moffatt, The Tutte polynomial of a delta-matroid and the world of graph polynomials

June 8: Relinde Jurrius, q-Analogues in combinatorics

June 8: Relinde Jurrius, q-Analogues in combinatorics

June 15: Rutger Campbell, Matroids doing algebra

June 22: Matthew Kwan, Halfway to Rota’s basis conjecture

July 6: Marthe Bonamy, Graph classes and their Asymptotic Dimension

July 13: Federico Ardila, Geometry of Matroids

July 20: Pascal Gollin, Obstructions for bounded branch-depth in matroids

July 20: Pascal Gollin, Obstructions for bounded branch-depth in matroids

July 27: Zach Walsh, Quadratically Dense Matroids

Aug 3: Jim Geelen, Towards the excluded-minors for GF(5)-representability

Aug 10: Yelena Yuditsky, Typical structure of hereditary graph families

Aug 17: Sophie Spirlk, A graph-based introduction to the chromatic symmetric function

Aug 10: Yelena Yuditsky, Typical structure of hereditary graph families

Aug 17: Sophie Spirlk, A graph-based introduction to the chromatic symmetric function

Aug 24: Ahmad Abdi, Ideal clutters and dyadic fractional packings

Aug 31: Tony Huynh, Subgraph densities in a surface

Sep 7: Matt Baker, Foundations of Matroids without Large Uniform Minors, Part 1

Sep 14: Oliver Lorscheid, Foundations of Matroids without Large Uniform Minors, Part 2

Sep 25

**:**Alexey Pokrovskiy, Rota’s Basis Conjecture holds asymptoticallySep 28: Daniel Cranston, Vertex Partitions into an Independent Set and a Forest with Each Component Small

Oct 5: Lorenzo Traldi, Isotropic matroids and circle graphs

Oct 19: Erik Panzer, The Hepp bound of a matroid: flags, volumes and integrals

Oct 26: Rose McCarty, Colouring pseudo-visibility graphs

Nov 2: Attila Joó, The Matroid Intersection Conjecture of Nash-Williams

Nov 9: James Davies, Geometric intersection graphs with large girth and chromatic number

Nov 16: Jakob Kneip, Tangles are decided by weighted vertex sets

Nov 23: Sarah Allred, Unavoidable induced subgraphs of large 2-connected graphs

Nov 30: Johannes Carmesin, Matroids and embedding graphs in surfaces

Dec 7: Sergey Norin, Densities of minor-closed graph classes

Dec 14:

**Open problems session**