Fig. 8

Example of a case ignored by the algorithm. At the top, the solution is obtained after juxtaposing a closeable alternating path \(p_1\) and absorbing a closeable alternating path \(p_2\). The intermediate solution is in the set \(\mathcal {A}'_+\) during the second step. Below, a solution of the same cardinality is obtained after absorbing \(p_1\) and juxtaposing \(p_2\) and in this case, the intermediate solution is in \(\mathcal {A}'\). The upper solution is not considered by the algorithm because the bottom solution has the same cardinality