Digraphs: Theory, Algorithms and Applications
Digraphs: Theory, Algorithms and Applications
Disjoint directed and undirected paths and cycles in digraphs
Theoretical Computer Science
Decomposing locally semicomplete digraphs into strong spanning subdigraphs
Journal of Combinatorial Theory Series B
Theoretical Computer Science
Note: Arc-disjoint paths and trees in 2-regular digraphs
Discrete Applied Mathematics
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We prove that a number of natural problems concerning the existence of arc-disjoint directed and ''undirected'' (spanning) subdigraphs in a digraph are NP-complete. Among these are the following of which the first settles an open problem due to Thomasse (see e.g. Bang-Jensen and Gutin (2009) [1, Problem 9.9.7] and Bang-Jensen and Kriesell (2009) [5,4]) and the second settles an open problem posed in Bang-Jensen and Kriesell (2009) [5]. *Given a directed graph D and a vertex s of D; does D contain an out-branching B"s^+ rooted at s such that the digraph remains connected (in the underlying sense) after removing all arcs of B"s^+? *Given a strongly connected directed graph D; does D contain a spanning strong subdigraph D^' such that the digraph remains connected (in the underlying sense) after removing all arcs of D^'?