@article{MZ_1977__153_172486,
     author = {Allan J. Sieradski},
     title = {A {Semigroup} of {Simple} {Homotopy} {Types.}},
     journal = {Mathematische Zeitschrift},
     pages = {135--148},
     publisher = {mathdoc},
     volume = {153},
     year = {1977},
     zbl = {0358.57006},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__153_172486/}
}