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

Prof. Emo Welzl and Prof. Bernd Gärtner

Mittagsseminar Talk Information |

**Date and Time**: Thursday, November 08, 2007, 12:15 pm

**Duration**: This information is not available in the database

**Location**: CAB G51

**Speaker**: Jan Foniok

Some polynomial cases of the Constraint Satisfaction Problem are characterised by the existence of a suitable complete set of obstructions. One of the polynomial cases is when there exists a complete set of obstructions that are all trees. In this case the template is said to have tree duality. If a digraph H has tree duality, then also its arc-graph delta(H) has tree duality.

A construction called Sproink is developed such that if H has tree duality, then the set of all Sproinks of all the tree obstructions for H is a complete set of tree obstructions for the arc-graph delta(H). Moreover, starting from digraphs with finite duality repeatedly using products and the arc-graph functor generates a class of digraphs with tree duality. These are definitely not all digraphs with tree duality (because all generated digraphs have the near-unanimity function and have bounded height of tree obstructions) but it remains to see what particular subclass this process actually generates.

Joint work with Claude Tardif.

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