Point partition numbers: Decomposable and indecomposable critical graphs
- In the present paper we extend the following three coloring concepts for the class of finite undirected graphs having multiple edges but no loops. First of all, the generalized coloring concept, in which the same colored vertices of a graph induce a subgraph satisfying a prescribed graph property. Secondly, the concept of variable degeneracy, which was introduced by Borodin, Kostochka and Toft in 2000; this makes it possible to give a common generalization of the point partition number and the list chromatic number. Finally, the DP-coloring concept as introduced by Ďvorák and Postle in 2018, where a list assignment of a graph is replaced by a cover. Combining these three coloring concepts leads to generalizations of various classical coloring results, including the theorems of Brooks, of Gallai, and of Erdős, Rubin and Taylor. Our main result is a DP-version of a theorem about partitions of graphs into a fixed number of induced subgraphs with bounded variable degeneracy due to Borodin, Kostochka, and Toft.
