@article{GDZPPN002187361,
title = {Compactness of the inverse of the minimal operator for a class of ordinary differential expressions.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {253},
year = {1972},
pages = {91-99},
zbl = {0248.34035},
url = {http://dml.mathdoc.fr/item/GDZPPN002187361}
}
Kauffman, Robert M. Compactness of the inverse of the minimal operator for a class of ordinary differential expressions.. Journal für die reine und angewandte Mathematik, Tome 253 (1972) pp. 91-99. http://gdmltest.u-ga.fr/item/GDZPPN002187361/