@article{MZM_1977_22_5_a3,
     author = {P. Ya. Grushko},
     title = {Morphisms of geometric structures},
     journal = {Matemati\v{c}eskie zametki},
     pages = {633--642},
     publisher = {mathdoc},
     volume = {22},
     number = {5},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1977_22_5_a3/}
}