Extending rational choice behavior: The decision problem for Boolean set theory with a choice correspondence

TL;DR

This paper explores the extension of partial choice functions to total ones within Boolean set theory, analyzing axioms of consistency and the computational complexity of related satisfiability problems.

Contribution

It characterizes conditions for extending partial choices to total choices satisfying economic axioms and studies the NP-completeness of the associated satisfiability problems.

Findings

Lifting partial choices to total choices is characterized for certain axioms.

Decidability of the satisfiability problem is established as NP-complete in key cases.

Complexity remains NP-complete when the number of choice terms is fixed.

Abstract

Given the family $P$ of all nonempty subsets of a set $U$ of alternatives, a choice over $U$ is a function $c \colon \Omega \to P$ such that $\Omega \subseteq P$ and $c(B) \subseteq B$ for all menus $B \in \Omega$. A choice is total if $\Omega = P$, and partial otherwise. In economics, an agent is considered rational whenever her choice behavior satisfies suitable axioms of consistency, which are properties quantified over menus. Here we address the following lifting problem: Given a partial choice satisfying one or more axioms of consistency, is it possible to extend it to a total choice satisfying the same axioms? After characterizing the lifting of some choice properties that are well-known in the economics literature, we study the decidability of the connected satisfiability problem for unquantified formulae of an elementary fragment of set theory, which involves a choice function symbol, the Boolean set operators, the singleton, the equality and inclusion predicates, and the propositional connectives. In two cases we prove that the satisfiability problem is NP-complete, whereas in the remaining cases we obtain NP-completeness under the additional assumption that the number of choice terms is constant.