@article{10_4153_CMB_1969_028_7,
     author = {Adams, Robert A.},
     title = {-\ensuremath{\Delta} is {Positive} {Definite} on a {"Spiny} {Urchin"}},
     journal = {Canadian mathematical bulletin},
     pages = {229--231},
     year = {1969},
     volume = {12},
     number = {2},
     doi = {10.4153/CMB-1969-028-7},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1969-028-7/}
}