@article{MM2_1990__68_2_155540,
     author = {Nancy Childress},
     title = {Examples of ...-invariants.},
     journal = {Manuscripta mathematica},
     pages = {447--453},
     publisher = {mathdoc},
     volume = {68},
     number = {2},
     year = {1990},
     zbl = {0711.11039},
     url = {http://geodesic.mathdoc.fr/item/MM2_1990__68_2_155540/}
}