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$%L. R. Berrone, Coalescence of measures and f-rearrangements of a function, Rev. Mat. Complut. 12 (1999), no. 2, 477509. %$

Coalescence of Measures and f-Rearrangements of a Function
Lucio R. BERRONE
Departamento de Matemática
Facultad de Ciencias Exactas, Ing. y Agrim.
Universidad Nacional de Rosario
Av. Pellegrini 250
2000 Rosario — Argentina

Received: January 11, 1999
 

ABSTRACT

This paper addresses the question of characterizing optimum values in the problem

sup{n(E) : m(E)< C},
                   (1)

where m  and n  are measures defined on a s  -finite measurable space X  . With this purpose, the f  -rearrangement of a function g  is introduced so as to formalize the idea of rearranging the level sets of the function g  according to how these sets are arranged in a given function f  . A characterization of optima of problem (1) is then obtained in terms of dn/dm  -rearrangements, dn/dm  being the Radon-Nikodým derivative of the measure n  with respect to m  . When X  is a topological space and m  , n  are Borel measures, we say that n  is coalescent with respect to m  when, for every C > 0  , there exist connected optima solving problem (1). A general criterion for coalescence is given and some simple examples are discussed.

1991 Mathematics Subject Classification: 49N99, 28A25, 26D10.