@article{10_21136_CMJ_1991_102502,
     author = {Chartrand, Gary and Tian, Song Lin},
     title = {Oriented graphs with prescribed $m$-center and $m$-median},
     journal = {Czechoslovak Mathematical Journal},
     pages = {716--723},
     publisher = {mathdoc},
     volume = {41},
     number = {4},
     year = {1991},
     doi = {10.21136/CMJ.1991.102502},
     mrnumber = {1134960},
     zbl = {0759.05033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1991.102502/}
}