1. Pereverzev, S.V., Optimizatsiya metodov priblizhennogo resheniya operatornykh uravnenii (Optimization of Approximation Methods for Operator Equations), Kiev, 1996.
2. Tikhomirov, V.M., Nekotorye voprosy teorii priblizhenii (Some Problems of Approximation Theory), Moscow, 1976.
3. Pereverzev, S.V. and Azizov, M., Ukr. Mat. Zh., 1996, vol. 48, no.5, pp. 656–665.
4. Kantorovich, L.V. and Akilov, G.P., Funktsional'nyi analiz (Functional Analysis), Moscow, 1977.