@article{CMUC_1980__21_4_a12,
     author = {Biryukov, Petr A.},
     title = {Cardinalities and ranks of $\pi$-bases in topological spaces},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {769--776},
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {1980},
     mrnumber = {597766},
     zbl = {0457.54003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1980__21_4_a12/}
}