Proof Pearl: Defining Functions over Finite Sets.

Structural recursion over sets is meaningful only if the result is independent of the order in which the set's elements are enumerated. This paper outlines a theory of function definition for finite sets, based on the fold functionals often used with lists. The fold functional is introduced as a relation, which is then shown to denote a function under certain conditions. Applications include summation and maximum. The theory has been formalized using Isabelle/HOL . [ABSTRACT FROM AUTHOR]