@article{BAG_1988__27_138419,
     author = {H.-D. Hecker and D. Herwig},
     title = {NP-harte {Probleme} f\"ur minimale {Polygon\"uberdeckungen}},
     journal = {Beitr\"age zur Algebra und Geometrie},
     pages = {161--164},
     publisher = {mathdoc},
     volume = {27},
     year = {1988},
     url = {http://geodesic.mathdoc.fr/item/BAG_1988__27_138419/}
}