VARIATIONAL METHOD FOR SOLVING BOUNDARY-VALUE-PROBLEMS FOR THE WAVE-EQUATION Статья FILIPPOV V.M. Differential Equations. Том 20. 1984. С. 1401-1407
HOKARTITE FROM THE SAN-JOSE DEPOSIT (BOLIVIA) Статья DOBROVOLSKAIA M.G., SANDI K.EA., MALOV V.S., VIALSOV L.N., BASOVA G.V. Doklady Akademii nauk SSSR. Mezhdunarodnaya Kniga, Moscow, Russian Federation. Том 275. 1984. С. 720-725