@article{CMJ_1997__47_1_a5,
     author = {Chartrand, Gary and Gavlas, Heather and Schulz, Kelly and Winters, Steve J.},
     title = {On strong digraphs with a prescribed ultracenter},
     journal = {Czechoslovak Mathematical Journal},
     pages = {83--94},
     publisher = {mathdoc},
     volume = {47},
     number = {1},
     year = {1997},
     mrnumber = {1435607},
     zbl = {0897.05033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMJ_1997__47_1_a5/}
}