call it, provides abstraction through the rewriting arrow and explicit rule application. It also embeds the notion of sets of results to deal with non-deterministic computations. Furthermore, the calculus is parameterized by the matching algorithm used in order to fire the rules. In its simplest instance, -calculus embeds standard first-order rewriting as well as -calculus. In the second part of the talk, we will introduce the -calculus and show how it provides a simple semantics for ELAN programs. References BKK+ 98. Peter Borovansk