Characterisations of $H^1$ by singular intetgral transforms on martingales and $\mathsf{R}^n$

S. Janson, “Characterisations of $H^1$ by singular intetgral transforms on martingales and $\mathsf{R}^n$”, Math. Scand., vol. 41, pp. 140–152, Dec. 1977, doi: 10.7146/math.scand.a-11708.