code: func (l *Locking) Perm(n int) (v []int) {
  	l.Lock()
  	v = l.R.Perm(n)
  	l.Unlock()
  	return
  }
docs: // Perm returns, as a slice of n ints, a pseudo-random permutation of the
  // integers [0,n) from the source in the context or the shared global source.