@article{10_21136_CPM_1986_118285,
     author = {Chrastina, Jan},
     title = {On formal theory of differential equations. {I}},
     journal = {\v{C}asopis pro p\v{e}stov\'an{\'\i} matematiky},
     pages = {353--383},
     publisher = {mathdoc},
     volume = {111},
     number = {4},
     year = {1986},
     doi = {10.21136/CPM.1986.118285},
     mrnumber = {871713},
     zbl = {0638.35008},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CPM.1986.118285/}
}