@article{MS2_1961__9_165769,
     author = {Nils Nilsson},
     title = {Some {Estimates} for {Eigenfunction} {Expansions} and {Spectral} {Functions} {Corresponding} to {Elliptic} {Differential} {Operators.}},
     journal = {Mathematica Scandinavica},
     pages = {107--121},
     publisher = {mathdoc},
     volume = {9},
     year = {1961},
     zbl = {0098.06801},
     url = {http://geodesic.mathdoc.fr/item/MS2_1961__9_165769/}
}