@article{MOMA_1976__81_177764,
     author = {Wolfgang Wertz},
     title = {Invariant {Density} {Estimation.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {315--324},
     year = {1976},
     volume = {81},
     zbl = {0361.62030},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1976__81_177764/}
}