Library /sys$common/syshlp/sda.hlb SET, PROCESS, /INDEX=n  *Conan The Librarian (sorry for the slow response - running on an old VAX)

     Specifies the new current process by the index into the system's
     list of software process control blocks (PCB).  Alternatively, this
     argument can be the process identification (EPID or PID) longword,
     from which SDA extracts the correct index.