Bañuelos R., Bogdan K., “Lévy processes and Fourier multipliers”, J. Funct. Anal., 250:1 (2007), 197–213
Dragičević O., Petermichl S., Volberg A., “A rotation method which gives linear $L^p$ estimates for powers of the Ahlfors-Beurling operator”, J. Math. Pures Appl. (9), 86:6 (2006), 492–509
Dragičević O., Volberg A., “Bellman functions and dimensionless estimates of Littlewood-Paley type”, J. Operator Theory, 56:1 (2006), 167–198
Dragičević O., Volberg A., “Bellman function, Littlewood-Paley estimates and asymptotics for the Ahlfors-Beurling operator in $L^p(\mathbb C)$”, Indiana Univ. Math. J., 54:4 (2005), 971–995
Dragičević O., Volberg A., “Bellman function for the estimates of Littlewood-Paley type and asymptotic estimates in the $p-1$ problem”, C. R. Math. Acad. Sci. Paris, 340:10 (2005), 731–734
Kari Astala, Tadeusz Iwaniec, Eero Saksman, “Beltrami operators in the plane”, Duke Math. J., 107:1 (2001)