Gunko, M. S., et al. “Optimal Recovery of Elements from Hilbert Space and Their Scalar Products by Fourier Coefficients Known With Error”. Ukrains’kyi Matematychnyi Zhurnal, vol. 72, no. 6, June 2020, pp. 736-50, https://doi.org/10.37863/umzh.v72i6.1107.