@article{ZNSL_2005_327_a2,
     author = {A. Vagharshakyan},
     title = {Invariant transformations for the {Sturm--Liouville} operator},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {25--54},
     publisher = {mathdoc},
     volume = {327},
     year = {2005},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2005_327_a2/}
}