@article{TMF_1975_25_1_a2,
     author = {G. V. Efimov},
     title = {On the proof that the $S$ matrix is unitary},
     journal = {Teoreti\v{c}eska\^a i matemati\v{c}eska\^a fizika},
     pages = {20--29},
     publisher = {mathdoc},
     volume = {25},
     number = {1},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/TMF_1975_25_1_a2/}
}