@article{10_21136_CMJ_1994_128448,
     author = {Vaughan, Jerry E.},
     title = {On {Frol{\'\i}k's} characterization of class $P$},
     journal = {Czechoslovak Mathematical Journal},
     pages = {1--6},
     publisher = {mathdoc},
     volume = {44},
     number = {1},
     year = {1994},
     doi = {10.21136/CMJ.1994.128448},
     mrnumber = {1257931},
     zbl = {0822.54003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1994.128448/}
}