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2. D. Borisov, “The spectrum of two quantum layers coupled by a window,” J. Phys. A. Math. Theor. 40, No. 19, 5045–5066 (2007).
3. D. I. Borisov, “Discrete spectrum of an asymmetric pair of waveguides coupled through a window” [in Russian], Mat. Sb. 197, No. 4, 3–32 (2006); English trans.: Sb. Math. 197, No. 4, 475-504 (2006).
4. S. A. Nazarov, “Asymptotics of an eigenvalue on the continuous spectrum of two quantum waveguides coupled through narrow windows” [in Russian], Mat. Zametki 93, No. 2, 227–245 (2013); English transl.: Math. Notes 93, No. 2, 266–281 (2013).
5. D. Borisov, P. Exner, and R. Gadyl’shin, “Geometric coupling thresholds in a twodimensional strip,” J. Math. Phys. 43, No. 12, 6265–6278 (2002).