TY CONF TI PROPERTIES OF MIXED MODULI OF SMOOTHNESS OF FUNCTIONS WITH MONOTONE FOURIER COEFFICIENTS KW metric KW mixed moduli of smoothness KW monotone Fourier coefficients JO OPERATOR EQUATIONS AND SOME RELATED ISSUES IN APPLIED MATHEMATICS AU Simonov, A.B. AU Simonov, B.V. PY 2026 PB FSBE Institution of Higher Education Voronezh State University of Forestry and Technologies named after G.F. Morozov