Czechoslovak Mathematical Journal, first online, pp. 1-31
Fundamental groupoids of digraphs and graphs
Alexander Grigor'yan, Rolando Jimenez, Yuri Muranov
Received December 18, 2015. First published January 15, 2018.
Abstract: We introduce the notion of fundamental groupoid of a digraph and prove its basic properties. In particular, we obtain a product theorem and an analogue of the Van Kampen theorem. Considering the category of (undirected) graphs as the full subcategory of digraphs, we transfer the results to the category of graphs. As a corollary we obtain the corresponding results for the fundamental groups of digraphs and graphs. We give an application to graph coloring.
Keywords: digraph; fundamental group; fundamental groupoid; product of graphs
Affiliations: Alexander Grigor'yan, Mathematics Department, University of Bielefeld, Universitätsstrasse 25, P. O. Box 100131, D-33501, Bielefeld, Germany, e-mail: firstname.lastname@example.org; Rolando Jimenez, Instituto de Matematicas, UNAM Unidad Oaxaca, Leon 2, Centro, 68000 Oaxaca, Mexico, e-mail: email@example.com; Yuri Muranov, Faculty of Mathematics and Computer Science, University of Warmia and Mazury, Sloneczna 54 Street, 10-710 Olsztyn, Poland, e-mail: firstname.lastname@example.org