@article{MS2_1956__4_165604,
     author = {EARL A. CODDINGTON},
     title = {On self-adjoint ordinary differential operators.},
     journal = {Mathematica Scandinavica},
     pages = {9--21},
     publisher = {mathdoc},
     volume = {4},
     year = {1956},
     zbl = {0074.06701},
     url = {http://geodesic.mathdoc.fr/item/MS2_1956__4_165604/}
}