@article{02100250,
title = {Exactly solvable and unsolvable shortest network problems in 3D-space.},
journal = {Beitr\"age zur Algebra und Geometrie},
volume = {45},
year = {2004},
pages = {649-663},
zbl = {1062.05037},
language = {en},
url = {http://dml.mathdoc.fr/item/02100250}
}
Booth, R.S.; Thomas, D.A.; Weng, J.F. Exactly solvable and unsolvable shortest network problems in 3D-space.. Beiträge zur Algebra und Geometrie, Tome 45 (2004) pp. 649-663. http://gdmltest.u-ga.fr/item/02100250/