@article{SM_1998_189_6_a1,
     author = {A. S. Lakhtin and A. I. Subbotin},
     title = {Multivalued solutions of first-order partial differential equations},
     journal = {Sbornik. Mathematics},
     pages = {849--873},
     publisher = {mathdoc},
     volume = {189},
     number = {6},
     year = {1998},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1998_189_6_a1/}
}