/sys$common/syshlp/helplib.hlb CC, Run-time functions, nice  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Increments or decrements the process priority relative to the
  process current priority by the amount of the argument.  A negative
  argument increments the priority; a positive argument decrements
  it.  Issuing nice(0) restores the base priority.  The resulting
  priority cannot be less than 1, or greater than the process's base
  priority.  This function is nonreentrant.

  Syntax:

       #include <unistd.h>

       nice(int increment);