Adamov, A. N. 2009. “Inequality of the Turan Type for Trigonometric Polynomials and Conjugate Trigonometric Polynomials in $L_0$”.
Ukrains’kyi Matematychnyi Zhurnal
61 (7): 986-95.
https://umj.imath.kiev.ua/index.php/umj/article/view/3073
.