@article{MOMA_1967__71_177392,
     author = {R.F. Albrecht and P. Vachenauer},
     title = {On the {Equivalence} of {Systems} of {Partial} {Differential} {Equations.}},
     journal = {Monatshefte f\"ur Mathematik},
     pages = {354--368},
     publisher = {mathdoc},
     volume = {71},
     year = {1967},
     zbl = {0148.34103},
     url = {http://geodesic.mathdoc.fr/item/MOMA_1967__71_177392/}
}