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@article{MV_1967_19_3_a20, author = {B. N. Rachajsky}, title = {On a variant in the theory of characteristics for systems of first order partial differential equations}, journal = {Matemati\v{c}ki vesnik}, pages = {329 }, publisher = {mathdoc}, volume = {19}, number = {3}, year = {1967}, url = {http://geodesic.mathdoc.fr/item/MV_1967_19_3_a20/} }
B. N. Rachajsky. On a variant in the theory of characteristics for systems of first order partial differential equations. Matematički vesnik, Tome 19 (1967) no. 3, p. 329 . http://geodesic.mathdoc.fr/item/MV_1967_19_3_a20/