@article{CMH_1991__66_4_140244,
     author = {L. Alessandrini and G. Bassanelli},
     title = {A balanced proper modification of {P3.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {505--511},
     publisher = {mathdoc},
     volume = {66},
     number = {4},
     year = {1991},
     zbl = {0761.53034},
     url = {http://geodesic.mathdoc.fr/item/CMH_1991__66_4_140244/}
}