@article{MZ_1933__37_168433,
     author = {F. Klein},
     title = {\"Uber gekoppelte {Axiomensysteme} in der {Theorie} der abstrakten {Verkn\"upfungen.}},
     journal = {Mathematische Zeitschrift},
     pages = {39--60},
     publisher = {mathdoc},
     volume = {37},
     year = {1933},
     zbl = {0006.38501},
     url = {http://geodesic.mathdoc.fr/item/MZ_1933__37_168433/}
}