Almost any sequential Prolog system is in principle easy to extend for OR-parallelism, using the Muse execution model. To reduce your programming effort we have implemented the Muse scheduler, with a clean interface to the Prolog sequential engine. This interface is implemented as a set of C macros. The sequential Prolog system to be parallelized uses some of those macros provided by the Muse scheduler and must also provide some macros for the Muse scheduler. This chapter paper contains a definition and description of the required macros, emphasizing information needed by the Prolog engine programmer.