We extend the classical theorems of I. I. Privalov and A. Zygmund from single to multiple conjugate functions in terms of the multiplicative modulus of continuity. A remarkable corollary is that if a function f belongs to the multiplicative Lipschitz class for some and its marginal functions satisfy for some uniformly in the indicated variables , 1 ≤ l ≤ N, then for each choice of with or 1 for 1 ≤ l ≤ N.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-cm115-1-3, author = {Ferenc M\'oricz}, title = {Multiple conjugate functions and multiplicative Lipschitz classes}, journal = {Colloquium Mathematicae}, volume = {116}, year = {2009}, pages = {21-32}, zbl = {1160.42004}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm115-1-3} }
Ferenc Móricz. Multiple conjugate functions and multiplicative Lipschitz classes. Colloquium Mathematicae, Tome 116 (2009) pp. 21-32. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-cm115-1-3/