Let f be a nonnegative submartingale and S(f) denote its square function. We show that for any λ > 0, , and the constant π/2 is the best possible. The inequality is strict provided ∥f∥₁ ≠ 0.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-ba57-1-9, author = {Adam Os\k ekowski}, title = {Weak Type Inequality for the Square Function of a Nonnegative Submartingale}, journal = {Bulletin of the Polish Academy of Sciences. Mathematics}, volume = {57}, year = {2009}, pages = {81-89}, zbl = {1173.60015}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-ba57-1-9} }
Adam Osękowski. Weak Type Inequality for the Square Function of a Nonnegative Submartingale. Bulletin of the Polish Academy of Sciences. Mathematics, Tome 57 (2009) pp. 81-89. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-ba57-1-9/