@article{SM_2001_192_3_a6,
     author = {V. I. Yudovich},
     title = {Periodic differential equations with self-adjoint monodromy operator},
     journal = {Sbornik. Mathematics},
     pages = {455--478},
     publisher = {mathdoc},
     volume = {192},
     number = {3},
     year = {2001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2001_192_3_a6/}
}