@article{10_4153_CMB_1987_056_x,
     author = {Yamashita, Shinji},
     title = {Derivatives and {Length-Preserving} {Maps}},
     journal = {Canadian mathematical bulletin},
     pages = {379--384},
     year = {1987},
     volume = {30},
     number = {3},
     doi = {10.4153/CMB-1987-056-x},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1987-056-x/}
}