@article{10_21136_MB_1991_126196,
     author = {Chrastina, Jan},
     title = {On formal theory of differential equations. {III.}},
     journal = {Mathematica Bohemica},
     pages = {60--90},
     publisher = {mathdoc},
     volume = {116},
     number = {1},
     year = {1991},
     doi = {10.21136/MB.1991.126196},
     mrnumber = {1100425},
     zbl = {0728.58041},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/MB.1991.126196/}
}