@article{10_4153_CMB_1974_029_1,
     author = {Schonheim, J.},
     title = {On {A} {Problem} of {Purdy} {Related} to {Sperner} {Systems}},
     journal = {Canadian mathematical bulletin},
     pages = {135--136},
     year = {1974},
     volume = {17},
     number = {1},
     doi = {10.4153/CMB-1974-029-1},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1974-029-1/}
}