@article{MAN_1971__195_162229,
     author = {H.O. Cordes},
     title = {Self-Adjointness of {Powers} of {Elliptic} {Operators} on {Non-Compact} {Manifolds.}},
     journal = {Mathematische Annalen},
     pages = {257--272},
     publisher = {mathdoc},
     volume = {195},
     year = {1971},
     zbl = {0235.47021},
     url = {http://geodesic.mathdoc.fr/item/MAN_1971__195_162229/}
}