@article{RSMUP_1971__45__223_0,
     author = {Chv\`al, V.},
     title = {Piani di {M\"obius} $k$-aperti},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {223--228},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {45},
     year = {1971},
     mrnumber = {308929},
     zbl = {0231.50020},
     language = {it},
     url = {http://archive.numdam.org/item/RSMUP_1971__45__223_0/}
}