A Type is a Type is a Type ?

We present an incremental constraint solver as the nucleus of a soft type checker for a higher-order concurrent constraint language. Designed as a variation of rational tree uniication, our algorithm additionally decides satissability of weak subtype constraints of the form xy. It allows for a number of extensions such as record types, sorts, union types, and type declarations, which we discuss by example. Hard disjunctive constraints are handeled as incomplete propagators which in-crementally make as many simple constraints explicit as feasible. These extensions let our algorithm become suitable for type checking of a full-edged programming language.