@article{10_21136_CMJ_1975_101317,
     author = {Hartfiel, Darald J. and Maxson, Carlton J.},
     title = {A matrix characterization of the maximal groups in $\beta_X$},
     journal = {Czechoslovak Mathematical Journal},
     pages = {274--278},
     publisher = {mathdoc},
     volume = {25},
     number = {2},
     year = {1975},
     doi = {10.21136/CMJ.1975.101317},
     mrnumber = {0369587},
     zbl = {0313.18007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1975.101317/}
}