Multimatroids. II: Orthogonality, minors and connectivity.
Parity systems and the delta-matroid intersection problem.
Bipartite graphs that are not circle graphs
The following result is proved: if a bipartite graph is not a circle graph, then its complement is not a circle graph. The proof uses Naji’s characterization of circle graphs by means of a linear system of equations with unknowns in . At the end of this short note I briefly recall the work of François Jaeger on circle graphs.
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