An ordered set of Nörlund means.
Analytic continuation by means of the methods of divergent series
Application of a Tauberian theorem to finite model theory.
Approximation by Abel means and Tauberian Theorems in sequences spaces
Approximation on the semi-infinite interval.
Axiomatic theory of divergent series and cohomological equations
A general theory of summation of divergent series based on the Hardy-Kolmogorov axioms is developed. A class of functional series is investigated by means of ergodic theory. The results are formulated in terms of solvability of some cohomological equations, all solutions to which are nonmeasurable. In particular, this realizes a construction of a nonmeasurable function as first conjectured by Kolmogorov.