@article{SF_1975__11_186352,
     author = {H.J. SHYR},
     title = {Some {Free} {Submonoids} of the {Free} {Monoid} of {Prefix} {Codes.}},
     journal = {Semigroup forum},
     pages = {22--29},
     publisher = {mathdoc},
     volume = {11},
     year = {1975},
     zbl = {0299.94005},
     url = {http://geodesic.mathdoc.fr/item/SF_1975__11_186352/}
}