1. W. Fushchych, W. Shtelen, and N. Serov, Symmetry Analysis and Exact Solutions of Nonlinear Mathematical Physics, Kluwer, Dordrecht (1993).
2. V. I. Fushchych, “How to extend the symmetry of equations?,” in: Symmetry and Solutions of Nonlinear Equations in Mathematical Physics [in Russian], Institute of Mathematics, Ukranian Academy of Sciences, Kiev (1987) pp. 4–16.
3. W. Fushchych and I. Tsyfra, “On a reduction and solutions of nonlinear wave equations with broken symmetry,” J. Phys. A, 20, 45–47 (1987).
4. V. I. Fushchych, N. I. Serov, and V. I. Chopik, “Conditional invariance and nonlinear solutions of the heat equation,” Dokl. Akad. Nauk Ukr. SSR, Ser. A, 9, 17–21 (1988).
5. G. W. Bluman and I. D. Cole, “The general similarity solution of the heat equation,” J. Math. Mech., 18, 1025–1042 (1969).