N.H. Bingham, C.M. Goldie and J.L. Teugels, Regular Variation, Cambridge University Press, 1987.
 L. de Haan, On regular variation and its applications to the weak convergence of sample extremes, Mathematical Centre Tracts, 32, 1970.
 W. Feller, An Introduction to Probability Theory and its Applications, John Wiley and Sons, Volume 2, 2nd Edition, 1971.
 J. Karamata, Sur un mode de croissance reguliere des fonctions, Mathematica (Cluj), 4 (1930), pp. 38-53.
 P. Kevei, On a conjecture of Seneta on regular variation of truncated moments, Publ. Inst. Math., 109 (2021), pp. 77-82.
 E. Omey, On the class gamma and related classes of functions, Publ. Inst. Math., 93 (2013), pp. 1-18.
 E. Omey and M. Cadena, New results on slowly varying functions in the Zygmund sense, Proc. Japan Acad., Ser. A, 96 (2020), pp. 45-49.
 B.A. Rogozin, The Distribution of the First Ladder Moment and Height and Fluctuation of a Random Walk, Theory Probab. Appl., 16 (1971), pp. 575-595.
 E. Seneta, Slowly varying functions in the Zygmund sense and generalized regular variation, J. Math. Anal. Appl., 475 (2019), pp. 1647-1657.
 R. Williamson, Multiply monotone functions and their Laplace transforms, Duke Math. J., 23 (1956), pp. 189-207.