1. N. I. Gerasimenko and B. S. Pavlov, “A Scattering Problem on Noncompact Graphs,” Teoret. Mat. Fiz. 74 (3), 345–359 (1988) [Theoret. and Math. Phys. {bd74} (3), 230–240 (1988)].
2. V. M. Babich and A.V. Poskryakov, “On Quasiphotons of Rayleigh Waves (the Case of an Anisotropic Elastic Body),” Zap. Nauchn. Sem. S.-Peterburg. Otdel. Mat. Inst. Steklov. (POMI) 332 (Mat. Vopr. Teor. Rasprostr. Voln 35), 7–18 (2006) [J. Math. Sci. (N. Y.) {bd142} (6), 2521–2527 (2007)].
3. V. M. Babich and V.V. Ulin, “The Complex Space-Time Ray Method and ‘Quasiphotons’,” Zap. Nauchn. Sem. Leningrad. Otdel. Mat. Inst. Steklov. (LOMI) 117 (Mathematical Questions in the Theory of Wave Propagation 12), 5–12 (1981).
4. Yu.V. Pokornyi, O. M. Penkin, V. L. Pryadiev, A. V. Borovskikh, K.P. Lazarev, and S. A. Shabrov, Differential Equations on Geometric Graphs (Fizmatlit, Moscow, 2004).
5. V. P. Maslov and M.V. Fedoryuk, Quasiclassical Approximation for the Equations of Quantum Mechanics (Nauka, Moscow, 1976) [V. P. Maslov and M. V. Fedoriuk, Semiclassical Approximation in Quantum Mechanics, Contemp. Math., 5 (D. Reidel, Dordrecht-Boston, 1981)].