On the occasion of Lars-Erik Persson's 65th birthday there was organized a conference Analysis, Inequalities and Homogenization Theory (AIHT), which was held at Lulea} University of Technology in June 8-11, 2009, in Lulea-Sweden. The first plenary lecture had the title above and here I present an abbreviated form of this lecture.
Banach J. Math. Anal.
4(1):
185-201
(2010).
DOI: 10.15352/bjma/1272374680