Recently I taught short courses on functional equations at several
universities (Barcelona, Bern, Graz, Hamburg, Milan, Waterloo). My aim
was to introduce the most important equations and methods of solution
through actual (not artifi- cial) applications which were recent and
with which I had something to do. Most of them happened to be related to
the social or behavioral sciences. All were originally answers to
questions posed by specialists in the respective applied fields. Here I
give a somewhat extended version of these lectures, with more recent
results and applications included. As previous knowledge just the basic
facts of calculus and algebra are supposed. Parts where somewhat more
(measure theory) is needed and sketches of lengthier calcula- tions are
set in fine print. I am grateful to Drs. J. Baker (Waterloo, Ont.), W.
Forg-Rob (Innsbruck, Austria) and C. Wagner (Knoxville, Tenn.) for
critical remarks and to Mrs. Brenda Law for care- ful computer-typing of
the manuscript (in several versions). A note on numbering of statements
and references: The numbering of Lemmata, Propositions, Theorems,
Corollaries and (separately) formulae starts anew in each section. If
quoted in another section, the section number is added, e.g. (2.10) or
Theorem 1.2. References are quoted by the last names of the authors and
the last two digits of the year, e.g. Daroczy-Losonczi [671. 1 1. An
aggregation theorem for allocation problems. Cauchy equation for
single-and multiplace functions. Two extension theorems.