“…Many other geometric magnitudes stay invariant in the sense that they don't get the variations of the first order (for example, the coefficients of the first fundamental form, Cristoffel's symbols, Gaussian curvature etc.). Many papers are devoted to the infinitesimal bending of curves, surfaces and manifolds (see (Aleksandrov, 1936;Efimov, 1948;Kon-Fossen, 1959;Vekua, 1959;Ivanova-Karatopraklieva & Sabitov, 1995;Velimirović, 2001a,b;Hinterleitner et al, 2008;Rančić et al, 2009;Alexandrov, 2010;Najdanović, 2015;Najdanović & Velimirović, 2017;Kauffman et al, 2019;Najdanović et al, 2019;Rančić et al, 2019;Rýparová & Mikeš, 2019;Belova et al, 2021;Maksimović et al, 2021).…”