Result:

• If the implicit procedure was found in the data set allocated to the SYSEXEC file, it is run as a REXX exec.
• If the implicit procedure was found in the data set allocated to the SYSPROC file, it is run as a REXX exec if the string REXX appears in a comment on line 1 of the procedure. Otherwise, it is run as a CLIST.

%mem4

runs "mem4" as REXX exec, if "mem4" was found in SYSEXEC or runs "mem4" as REXX exec or CLIST, depending on what is found in line 1 of procedure "mem4", if "mem4" was found in SYSPROC.