On factorization of Fefferman's inequality. (English). In: Došlá, Z., Kuben, J. and Vosmanský, J. (eds.): Proceedings of Equadiff 9, Conference on Differential Equations and Their Applications, Brno, August 25-29, 1997. [Part 3] Papers. Masaryk University, Brno, 1998. pp. 181-191