Solving Algebraic Equations Using Coalgebra

¹ Mathematics and Computer Science, University of Leicester; fdm2@mcs.le.ac.uk., ng13@mcs.le.ac.uk.
² FB 3 – Mathematics and Computer Science, Universität Bremen; cxl@tzi.de.

Received: 8 November 2002
Accepted: 6 August 2003

Abstract

Algebraic systems of equations define functions using recursion where parameter passing is permitted. This generalizes the notion of a rational system of equations where parameter passing is prohibited. It has been known for some time that algebraic systems in Greibach Normal Form have unique solutions. This paper presents a categorical approach to algebraic systems of equations which generalizes the traditional approach in two ways i) we define algebraic equations for locally finitely presentable categories rather than just Set; and ii) we define algebraic equations to allow right-hand sides which need not consist of finite terms. We show these generalized algebraic systems of equations have unique solutions by replacing the traditional metric-theoretic arguments with coalgebraic arguments.