The problem of recognizing whether a subset of attributes is a premise of a minimal cover of functional dependencies of a relation is shown to be coNP-complete. The complexity of some related decision, enumerating, and sampling problems on functional dependencies, FCA implications, and closed sets of attributes is discussed.
Given a set X, a König graph G for X is a graph with the following property: for every induced subgraph H of G, the maximum number of vertex-disjoint induced subgraphs from X in H is equal to the minimum number of vertices whose deletion from H results in a graph containing no graph in X as an induced subgraph. The purpose of this paper is to characterize all König graphs for X, where X has only the 3-path or X consists of the 3-path and 3-cycle. We give also polynomial-time algorithms for the recognition of König graphs for the 3-path and for finding the corresponding packing and cover numbers in graphs of this type.
We study the vertex coloring problem in classes of graphs defined by finitely many forbidden induced subgraphs. Of our special interest are the classes defined by forbidden induced subgraphs with at most 4 vertices. For all but three classes in this family we show either NP-completeness or polynomial-time solvability of the problem. For the remaining three classes we prove fixed-parameter tractability. Moreover, for two of them we give a 3/2 approximation polynomial algorithm.