Czechoslovak Mathematical Journal, Vol. 76, No. 1, pp. 17-29, 2026


A note on the Krausz theorem and the Whitney theorem for mixed line graphs

Zoran STANIĆ

Received November 24, 2024.   Published online January 15, 2026.

Abstract:  A mixed line graph of a mixed graph generalizes the notion of a line graph of an ordinary graph. The Krausz theorem on covering characterization of line graphs and a restricted variant of the Whitney theorem on isomorphism are formulated and proved in the framework of mixed line graphs. Moreover, we extend the notion of a mixed graph by allowing the existence of edges that are oriented away from each of their ends. The mentioned theorems are formulated and proved in this setting, as well.
Keywords:  mixed graph; oriented edge; bi-oriented edge; Krausz characterization; Whitney isomorphism
Classification MSC:  05C20, 05C22, 05C76


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Affiliations:   Zoran Stanić, Faculty of Mathematics, University of Belgrade, Studentski trg 16, 11158 Belgrade, Serbia e-mail: zstanic@matf.bg.ac.rs


 
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