After a minor change to Lemma 3.2,

After a minor change to Lemma 3.2, as follows, the proof of Theorem 5.1 works. In Lemma 3.2, path P˜ ends either before the last edge of P , if non-negative, or before the last interval of consecutive negative edges, otherwise. The discussion of the concluding remark in the proof of Theorem 5.1 remains valid due to the scanning the negative edges by Plain_scan intopological order.