4 papers
A Trivariate Dichromate Polynomial for Digraphs
Winfried Hochstättler, Johanna Wiehe
We define a trivariate polynomial combining the NL-coflow and the NL-flow polynomial, which build a dual pair counting acyclic colorings of directed graphs, in the more general set…
The Chromatic Polynomial of a Digraph
Winfried Hochstättler, Johanna Wiehe
An acyclic coloring of a digraph as defined by Neumann-Lara is a vertex-coloring such that no monochromatic directed cycles occur. Counting the number of such colorings with co…
A Semi-strong Perfect Digraph Theorem
Stephan Dominique Andres, Helena Bergold, Winfried Hochstättler +1
Reed showed that, if two graphs are -isomorphic, then either both are perfect or none of them is. In this note we will derive an analogous result for perfect digraphs.
The NL-flow polynomial
Barbara Altenbokum, Winfried Hochstättler, Johanna Wiehe
In 1982 Víctor Neumann-Lara introduced the dichromatic number of a digraph as the smallest integer such that the vertices of can be colored with colors and each…