@article{SLC_1989_21_a8,
     author = {Roman K\"onig},
     title = {\"Uber freie partiell kommutative {Monoide}},
     journal = {S\'eminaire lotharingien de combinatoire},
     publisher = {mathdoc},
     volume = {21},
     year = {1989},
     url = {http://geodesic.mathdoc.fr/item/SLC_1989_21_a8/}
}