@article{DAN_1965_163_6_a16,
     author = {Ya. B. Zel'dovich},
     title = {The number of quanta as an invariant of classical electromagnetic field},
     journal = {Doklady Akademii Nauk},
     pages = {1359--1360},
     publisher = {mathdoc},
     volume = {163},
     number = {6},
     year = {1965},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1965_163_6_a16/}
}