1. Beurling A.: Analyticity and difference estimates, collected works of Arne Beurling, vol. 1. In: Carleson, L., Malliavin, P., Neuberger, J., Wermer, J.(eds) Complex Analysis, Birkäuser, Basel (1989)
2. Beurling A.: On analytic extensions of semigroups of operators. J. Func. Anal. 6, 387–400 (1970)
3. Bernstein S.G., de La Vallée Poussin C.: L’Approximation. Chelsea Publishing Company, New York (1970)
4. Gasper G., Rahman M.: Basic hypergeometric series. Encyclopedia of Mathematics and its Applications 34. Cambridge University Press, Cambridge (1990) Zbl 0695.33001
5. Kemperman J.H.B.: On the regularity of generalized convex functions. Trans. Am. Math. Soc. 135, 69–93 (1969) Zbl 0183.32004