feder, 1991, Fractals
zornmerfeld, 1950, Partial differential equations of physics, Izd in lit
10.1088/0305-4470/30/21/006
10.1007/BF01036529
10.1016/0893-9659(96)00089-4
samko, 1987, Fractional Integrals and Derivatives and Some of Their Applications
tikhonov, 1977, Equations of Mathematical Physics