@article{SF_1991__42_3_135070,
     author = {T. Head and W. Forys},
     title = {Retracts of free monoids are nowhere dense with respect to finite group topologies and p-adic topologies.},
     journal = {Semigroup forum},
     pages = {117--120},
     publisher = {mathdoc},
     volume = {42},
     number = {3},
     year = {1991},
     zbl = {0721.68035},
     url = {http://geodesic.mathdoc.fr/item/SF_1991__42_3_135070/}
}