@article{10_21136_CPM_1989_118369,
     author = {Chrastina, Jan},
     title = {On formal theory of differential equations. {II}},
     journal = {\v{C}asopis pro p\v{e}stov\'an{\'\i} matematiky},
     pages = {60--105},
     publisher = {mathdoc},
     volume = {114},
     number = {1},
     year = {1989},
     doi = {10.21136/CPM.1989.118369},
     mrnumber = {0990119},
     zbl = {0703.34001},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CPM.1989.118369/}
}