More forbidden minors for Wye-Delta-Wye reducibily
- Author(s): Yu, Yaming;
- et al.
A graph is Y Delta Y reducible if it can be reduced to isolate vertices by a sequence of series-parallel reductions and Y Delta Y transformations. It is still an open problem to characterize Y Delta Y transformations. It is still an open problem to characterize Y Delta Y reducible graphs in terms of a finite set of forbidden minors. We obtain a characterization of such forbidden minors that can be written as clique kappa-sums for kappa = 1, 2, 3. As a result we show constructively that the total number of forbidden minors is more than 68 billion up to isomorphism.