Essén, Matts. 1990. “A Generalization of the M. Riesz Theorem on Conjugate Functions and the Zygmung LlogL -Theorem to Rd, D ≥ 2”.
Annales Fennici Mathematici
15 (1):83-105. https://doi.org/10.5186/aasfm.1990.1509.