1. [8] R. Durrett, Brownian motion and martingales in analysis, Wadsworth Mathematics Series, Wadsworth International Group, Belmont, CA, 1984.
2. [1] K. Astala, Area distortion of quasiconformal mappings, Acta Math. 173 (1994), no. 1, 37–60.
3. [2] Baernstein and J. Manfredi, Topics in quasiconformal mapping, Topics in modern harmonic analysis, Vol. I, II (Turin/Milan, 1982), Ist. Naz. Alta Mat. Francesco Severi, Rome, 1983, pp. 819–862.
4. [3] R. Bañuelos, Martingale transforms and related singular integrals, Trans. Amer. Math. Soc. 293 (1986), no. 2, 547–563.
5. [4] R. Bañuelos, A sharp good-$\lambda$ inequality with an application to Riesz transforms, Michigan Math. J. 35 (1988), no. 1, 117–125.