@article{SF_1976__13_134225,
     author = {K.D.  jr. Magill and S. Schanuel},
     title = {Sch\"utzenberger groups and {Chebyshev} polynomials.},
     journal = {Semigroup forum},
     pages = {301--306},
     year = {1976},
     volume = {13},
     zbl = {0354.20052},
     url = {http://geodesic.mathdoc.fr/item/SF_1976__13_134225/}
}