A simplification in the proof of the non-isomorphism between $H^1(\delta )$ and $H^1(\delta ^2)$
Studia Mathematica 150 (2002), 13-16 MSC: 30D55, 46B03, 60G46. DOI: 10.4064/sm150-1-2
The proof that $H^1(\delta )$ and $H^1(\delta ^2)$ are not isomorphic is simplified. This is done by giving a new and simple proof to a martingale inequality of J. Bourgain.