@article{MZM_1970_8_1_a13,
     author = {I. I. Tugov},
     title = {$P$-separation of variables in {Laplace's} equation},
     journal = {Matemati\v{c}eskie zametki},
     pages = {121--127},
     publisher = {mathdoc},
     volume = {8},
     number = {1},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1970_8_1_a13/}
}