@article{MZ_1990__203_3_174153,
     author = {Ben de Pagter},
     title = {A {Note} on a {Paper} by {W.J.} {Ricker} and {H.H.} {Schaefer.}},
     journal = {Mathematische Zeitschrift},
     pages = {645--648},
     publisher = {mathdoc},
     volume = {203},
     number = {3},
     year = {1990},
     zbl = {0669.47026},
     url = {http://geodesic.mathdoc.fr/item/MZ_1990__203_3_174153/}
}