@article{MM2_1975__16_154351,
     author = {T. Ando and K. Okubo},
     title = {Constants {Related} to {Operators} of {Class} {Cp.}},
     journal = {Manuscripta mathematica},
     pages = {385--394},
     publisher = {mathdoc},
     volume = {16},
     year = {1975},
     zbl = {0325.47008},
     url = {http://geodesic.mathdoc.fr/item/MM2_1975__16_154351/}
}