This specifies that the RSL parallel runtime library will be used to handle interprocessor communication, nesting, domain decomposition, etc. RSL is copyright Argonne National Laboratory and the Univerisity of Chicago but the agreement stipulates its free use and distribution. RSL is distributed as part of the MM5 source code in the MPP.TAR.gz distribution file. In other words, you already have it. If you are using the DM-parallel option to MM5, be sure pick up the latest MPP.TAR.gz file along with the mm5v2.tar.Z file when you upgrade to new versions.