@article{MS2_1957__5_165664,
     author = {GUNNAR BERGENDAL},
     title = {On spectral functions belonging to an elliptic differential operator with variable coefficients},
     journal = {Mathematica Scandinavica},
     pages = {241--254},
     year = {1957},
     volume = {5},
     zbl = {0080.30701},
     url = {http://geodesic.mathdoc.fr/item/MS2_1957__5_165664/}
}