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2. P. K. Rashevskii, A Course in Differential Geometry, 5th ed. (LKI, Moscow, 2008) [in Russian].
3. A. V. Pogorelov, Geometric Methods in the Nonlinear Theory of Elastic Shells (Nauka, Moscow, 1967) [in Russian].
4. M. I. Shtogrin, “Piecewise Smooth Developable Surfaces,” Tr. Mat. Inst. im. V.A. Steklova, Ross. Akad. Nauk 263, 227–250 (2008) [Proc. Steklov Inst. Math. 263, 214–235 (2008)].