@article{SF_1992__44_1_135139,
     author = {S. Margolis and C.J. Meakin},
     title = {Inverse monoids and rational {Schreier} subsets of the free group.},
     journal = {Semigroup forum},
     pages = {137--148},
     publisher = {mathdoc},
     volume = {44},
     number = {1},
     year = {1992},
     zbl = {0757.20017},
     url = {http://geodesic.mathdoc.fr/item/SF_1992__44_1_135139/}
}