The page-number of a directed acyclic graph (a DAG, for short) is the minimum k which DAG has topological order and k-coloring its edges such that no two same color cross, i.e., have alternating endpoints along order. In 1999, Heath Pemmaraju conjectured recognition DAGs with 2 NP-complete proved recognizing 6 [SIAM J. Computing, 1999]. Binucci et al. recently strengthened this result by provin...

This is a summary of the proof by G.E. Coxson [1] that P-matrix recognition is co-NP-complete. The result follows by a reduction from the MAX CUT problem using results of S. Poljak and J. Rohn [5].

The data-complexity of both satisfiability and finite satisfiability for the two-variable fragment with counting is NP-complete; the data-complexity of both query-answering and finite query-answering for the two-variable guarded fragment with counting is co-NP-complete.

Checking copositivity of a matrix is a co-NP-complete problem. This paper studies copositive matrices with certain spectral properties. It shows that an indefinite matrix with exactly one positive eigenvalue is copositive if and only if the matrix is nonnegative. Moreover, it shows that finding out if a matrix with exactly one negative eigenvalue is strictly copositive or not can be formulated ...

This is a summary of the proof by G.E. Coxson [1] that P-matrix recognition is co-NP-complete. The result follows by a reduction from the MAX CUT problem using results of S. Poljak and J. Rohn [5].

Two vertices in a graph are called an even pair (odd pair) if all induced paths between these two vertices have even (odd) length. Even and odd pairs have turned out to be of importance in conjunction with perfect graphs. We will characterize all linegraphs of bipartite graphs that contain an even resp. odd pair. In general, it is a co-NP-complete problem to decide whether a graph contains an e...

We investigate the complexity of the MEMBERSHIP problem for some geometrically deened classes of Boolean functions, i.e., the complexity of deciding whether a Boolean function given in DNF belongs to the class. We give a general argument implying that this problem is co-NP-hard for any class having some rather benign closure properties. Applying this result we show that the MEMBERSHIP problem i...

An important but strongly NP-hard problem in automated cartography is how to best place textual labels for point features on a static map. We examine the complexity of various generalizations of this problem for dynamic and/or interactive maps. Specifically, we show that it is strongly PSPACE-complete to decide whether there is a smooth dynamic labeling (function from time to static labelings) ...