@article{NSJOM_2004_34_2a_9,
     author = {J. Koppitz},
     title = {Hypersubstitutions and groups},
     journal = {Novi Sad Journal of Mathematics},
     pages = {127-139},
     publisher = {mathdoc},
     volume = {34},
     number = {2},
     year = {2004},
     url = {http://geodesic.mathdoc.fr/item/NSJOM_2004_34_2a_9/}
}