Network Flows : Theory, Algorithms, and Applications A generalized permanent labeling algorithm for the shortest path problem with time windows, Information Systems and Operations Research, vol.26, pp.191-212, 1988. ,
Fast and simple approximation schemes for generalized flow, Proceedings of the 10th annual ACM-SIAM Symposium on Discrete Mathematics, 1999. ,
DOI : 10.1007/s101070100238