ANZIAM  J.  44 (2003), 323-337
Additive selections and the stability of the Cauchy functional equation

Roman Badora
  Institute of Mathematics
  Silesian University
  ul. Bankowa 14
  PL-40-007 Katowice
  Poland
    robadora@gate.math.us.edu.pl
Roman Ger
  Institute of Mathematics
  Silesian University
  ul. Bankowa 14
  PL-40-007 Katowice
  Poland
    romanger@cto.us.edu.pl
and
Zsolt Páles
  Institute of Mathematics and Informatics
  University of Debrecen
  H-4010 Debrecen, Pf. 12
  Hungary
    pales@math.klte.hu


Abstract
The main result of this paper offers a necessary and sufficient condition for the existence of an additive selection of a weakly compact convex set-valued map defined on an amenable semigroup. As an application, we obtain characterisations of the solutions of several functional inequalities, including that of quasi-additive functions.
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