@article{IM_1984__78_143167,
     author = {W. Singhof},
     title = {The d-invariant of compact nilmanifolds.},
     journal = {Inventiones mathematicae},
     pages = {113--116},
     publisher = {mathdoc},
     volume = {78},
     year = {1984},
     zbl = {0558.55009},
     url = {http://geodesic.mathdoc.fr/item/IM_1984__78_143167/}
}