In this paper we describe the promoted tyft tyxt rule format for de ning higher-order languages. The rule format is a generalization of Groote and Vaandrager's tyft tyxt format in which terms are allowed as labels on transitions in rules. We prove that bisimulation is a congruence for any language de ned in promoted tyft tyxt format and demonstrate the usefulness of the rule format by presenting promoted tyft tyxt de nitions for the lazy -calculus, CHOCS and the -calculus.
Karen L. Bernstein