Bounding signed series-parallel graphs and cores of signed K 4 -subdivisions
Résumé
We study homomorphism properties of signed K4-minor-free graphs. On the one hand we give a necessary and sufficient condition for a signed graph B to admit a homomorphism from any signed K4-minor-free graph and we determine the smallest of all such signed graphs. On the other hand, we characterize the minimal cores that do not belong to the class of signed K4-minor-free graphs. This, in particular, gives a classification of odd-K4's that are cores. Furthermore, we show some applications of our work.
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