@article{MOMA_1988__106_1_178401,
     author = {G\"unter Lettl},
     title = {Subsemigroups of {Finitely} {Generated} {Groups} with {Divisor-Theory.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {205--210},
     publisher = {mathdoc},
     volume = {106},
     number = {1},
     year = {1988},
     zbl = {0671.20059},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1988__106_1_178401/}
}