@article{VMUMM_1990_5_a20,
     author = {A. D. Chanyshev},
     title = {Regular words and the sandwich-algebra theorem},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {84--85},
     year = {1990},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1990_5_a20/}
}