1. [19] E. M. Stein, Singular integrals and differentiability properties of functions, Princeton Mathematical Series, No. 30, Princeton University Press, Princeton, N.J., 1970.
2. [18] L. P. Rothschild and E. M. Stein, Hypoelliptic differential operators and nilpotent groups, Acta Math. 137 (1976), no. 3-4, 247–320.
3. [17] M. Reed and B. Simon, Methods of modern mathematical physics. II. Fourier analysis, self-adjointness, Academic Press [Harcourt Brace Jovanovich Publishers], New York, 1975.
4. [1] L. Carleson, Two remarks on $H\sp1$ and BMO, Advances in Math. 22 (1976), no. 3, 269–277.
5. [2] S. Y. A. Chang and R. Fefferman, A continuous version of duality of $H\sp1$ with BMO on the bidisc, Ann. of Math. (2) 112 (1980), no. 1, 179–201.