@article{1104253397, author = {Nelson, J. E. and Regge, T.}, title = {Invariants of $2+1$ gravity}, journal = {Comm. Math. Phys.}, volume = {151}, number = {1}, year = {1993}, pages = { 561-568}, language = {en}, url = {http://dml.mathdoc.fr/item/1104253397} }
Nelson, J. E.; Regge, T. Invariants of $2+1$ gravity. Comm. Math. Phys., Tome 151 (1993) no. 1, pp. 561-568. http://gdmltest.u-ga.fr/item/1104253397/