@article{RM_1970_25_6_a12,
     author = {V. P. Maslov},
     title = {A~generalization of the concept of characteristics for $A$-pseudodifferential operators with operator-valued symbol},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     year = {1970},
     volume = {25},
     number = {6},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/RM_1970_25_6_a12/}
}