@article{JSFU_2013_6_4_a14,
     author = {Isaac I. Vainshtein},
     title = {Model problems for two nonlinear equations that type depends on the solution},
     journal = {\v{Z}urnal Sibirskogo federalʹnogo universiteta. Matematika i fizika},
     pages = {539--547},
     publisher = {mathdoc},
     volume = {6},
     number = {4},
     year = {2013},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/JSFU_2013_6_4_a14/}
}