Consider the sequence of positive numbers defined by C₁ = 1 and , n = 1,2,.... Let M be a real-valued martingale and let S(M) denote its square function. We establish the bound |Mₙ|≤ Cₙ Sₙ(M), n=1,2,..., and show that for each n, the constant Cₙ is the best possible.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-ba61-2-11, author = {Adam Os\k ekowski}, title = {Moment Inequality for the Martingale Square Function}, journal = {Bulletin of the Polish Academy of Sciences. Mathematics}, volume = {61}, year = {2013}, pages = {169-180}, zbl = {1302.60072}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-ba61-2-11} }
Adam Osękowski. Moment Inequality for the Martingale Square Function. Bulletin of the Polish Academy of Sciences. Mathematics, Tome 61 (2013) pp. 169-180. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-ba61-2-11/