@article{CMUC_1967__8_3_a6,
     author = {Havel, V\'aclav},
     title = {Nets and groupoids},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {435--451},
     publisher = {mathdoc},
     volume = {08},
     number = {3},
     year = {1967},
     mrnumber = {0223956},
     zbl = {0162.24001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1967__8_3_a6/}
}