@article{MOMA_1981__91_178023,
     author = {Josef Hofbauer},
     title = {A {General} {Cooperation} {Theorem} for {Hypercycles.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {233--240},
     publisher = {mathdoc},
     volume = {91},
     year = {1981},
     zbl = {0449.34039},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1981__91_178023/}
}