Abstract:
It is proved that if a series in the Franklin system converges almost everywhere to a function $f(t)$ and the distribution function of the majorant of partial sums satisfies the condition
$$
\operatorname{mes}\bigl\{t\in[0,1]:s(t)>\lambda\bigr\}
=o\biggl(\frac 1\lambda\biggr)
$$
as $\lambda\to\infty$, then this series is a Fourier series for Lebesgue integrable functions $f(t)$. In the general case the coefficients of the series are reconstructed by means of an $A$-integral.