1. Hearn A. C., 1991. Reduce 3.4. User's manual: Rand Corp.
2. First-order perturbation method for anisotropic media
3. Petrashen G. I., Kashtan B. M. and Kovtun A. A., 1984. Volume waves propagation and methods of wave fields calculation in anisotropic elastic media. Leningrad, “Science” (in Russian).
4. Weak elastic anisotropy