Department of Computer Science | Institute of Theoretical Computer Science | CADMO

Theory of Combinatorial Algorithms

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar (in cooperation with A. Steger, D. Steurer and B. Sudakov)

Mittagsseminar Talk Information

Date and Time: Thursday, January 10, 2013, 12:15 pm

Duration: 30 minutes

Location: OAT S15/S16/S17

Speaker: Jan Foniok (Queen's University)

Adjoint functors in graph theory

Theorem (Geller, Stahl): Let G be a graph. Then the lexicographic product G[K2] is n-colourable if and only if G admits a homomorphism to the Kneser graph K(n,2).

Theorem (El-Zahar, Sauer): For two graphs G and H, the categorial product G × H is n-colourable if and only if G admits a homomorphism to the exponential graph KnH.

What do these two theorems have in common? Each is an example of the same phenomenon, known in category theory as adjoint functors. I will explain what they are and show some other applications, such as a circular version of the Gallai–Roy (–Hasse–Vitaver) Theorem.


Upcoming talks     |     All previous talks     |     Talks by speaker     |     Upcoming talks in iCal format (beta version!)

Previous talks by year:   2024  2023  2022  2021  2020  2019  2018  2017  2016  2015  2014  2013  2012  2011  2010  2009  2008  2007  2006  2005  2004  2003  2002  2001  2000  1999  1998  1997  1996  

Information for students and suggested topics for student talks


Automatic MiSe System Software Version 1.4803M   |   admin login