@article{MZ_1978__164_172785,
     author = {Ronald Hirshon},
     title = {Descending {Chains} in {Free} {Products.}},
     journal = {Mathematische Zeitschrift},
     pages = {293--296},
     publisher = {mathdoc},
     volume = {164},
     year = {1978},
     zbl = {0379.20036},
     url = {http://geodesic.mathdoc.fr/item/MZ_1978__164_172785/}
}