Motivation for including relational constraints other than equality within grammatical formalisms has come from discontinuous constituency and partially free word order for natural languages as well as from the need to define combinatory operations at the most basic level for languages with a two-dimensional syntax (., mathematical notation, chemical equations, and various diagramming languages). This paper presents F-PATR, a generalization of the PATR-II unification-based formalism, which incorporates relational constraints expressed as user-defined functions. .
