2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/119245We generalize five theorems of Leindler on the relations among Fourier coefficients and sum-functions under the more general $NBV$ condition.17 pages, Accepted by Studia Sci. Math. HungarClassical Analysis and ODEs42A32; 42A16text