@article{SF_1990__40_1_135002,
     author = {A. Geroldinger and G. Lettl},
     title = {Factorization problems in semigroups.},
     journal = {Semigroup forum},
     pages = {23--38},
     publisher = {mathdoc},
     volume = {40},
     number = {1},
     year = {1990},
     zbl = {0693.20063},
     url = {http://geodesic.mathdoc.fr/item/SF_1990__40_1_135002/}
}