1. J. Bourgain,Averages in the plane over convex curves and maximal operators, Journal d’Analyse Mathématique47 (1986), 69–85.
2. M. Cowling,On Littlewood-Paley-Stein theory, Rendiconti del Circolo Matematico di Palermo1 (1981), 21–55.
3. S. Cuccagna,L 2 estimates for averaging operators along curves with two-sided k-fold singularities, Duke Mathematical Journal89 (1997), 203–216.
4. G. Folland and E. M. Stein,Hardy Spaces on Homogeneous Groups, princeton University Press, 1982.
5. A. Greenleaf and A. Seeger,Fourier integral operators with fold singularities, Journal für die reine und angewandte Mathematik455 (1994), 35–56.