@article{CMUC_2006__47_4_a1,
     author = {Stronkowski, Micha{\l} Marek},
     title = {On free modes},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {561--568},
     publisher = {mathdoc},
     volume = {47},
     number = {4},
     year = {2006},
     mrnumber = {2337411},
     zbl = {1150.08304},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_2006__47_4_a1/}
}