@article{MOMA_1981__91_178012,
     author = {P. Kirschenhofer and G. Baron},
     title = {Operatorenkalk\"ul \"uber freien {Monoiden} {I:} {Strukturen.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {89--104},
     publisher = {mathdoc},
     volume = {91},
     year = {1981},
     zbl = {0447.05006},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1981__91_178012/}
}