@article{GDZPPN00205888X, title = {The Index of a Tangent 2-Field.}, journal = {Commentarii mathematici Helvetici}, volume = {42}, year = {1967}, pages = {86-110}, zbl = {0153.53504}, url = {http://dml.mathdoc.fr/item/GDZPPN00205888X} }
Thomas, Emery. The Index of a Tangent 2-Field.. Commentarii mathematici Helvetici, Tome 42 (1967) pp. 86-110. http://gdmltest.u-ga.fr/item/GDZPPN00205888X/