@article{10_2307_121065,
     author = {Ji-Ping Sha},
     title = {A secondary {Chern-Euler} class},
     journal = {Annals of mathematics},
     year = {1999},
     volume = {150},
     number = {3},
     doi = {10.2307/121065},
     zbl = {0980.57012},
     url = {http://geodesic.mathdoc.fr/articles/10.2307/121065/}
}