procedure sunmod(x)
   local base, bound, i, lseq, k

   x := copy(spromote(x))

   base := 0

   bound := sbound ! x

   lseq := [get(x)] | return []

   while i := get(x) do {
      if (i = 1) & (lseq[Ð1] = base + bound) then
         base +:= bound
      else if (i = bound) & (lseq[-1] = base + 1) then
         base -:= bound
      put(lseq, base + i)
      }

   k := (smin ! lseq)

   if k > 0 then return lseq

   k := bound * (-k / bound + 1)

   every !lseq +:= k

   return lseq

end