@article{JRAM_1991__416_153313,
     author = {G\"unter Stolz},
     title = {On the absolutely continuous spectrum of perturbed periodic {Sturm-Liouville} operators.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {1--24},
     year = {1991},
     volume = {416},
     zbl = {0716.34028},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1991__416_153313/}
}