@article{olevskii:1950:tsi,
    author = {Olevski{\u\i}, M. N.},
     title = {Triorthogonal systems in spaces of constant curvature in which
              the equation $\Delta_{2} u+\lambda u=0$ allows a complete
              separation of variables},
   journal = {Mat. Sbornik N.S.},
    volume = {27(69)},
    number = {3},
      year = {1950},
     pages = {379–426},
  language = {Russian},
      note = {In Russian.},
   mrclass = {36.0X},
  mrnumber = {MR0038535 (12,415b)},
mrreviewer = {H. Busemann},
     zblno = {0041.49802}}