MAYBE
Trs:
 {   sqr(x) -> *(x, x),
   sum(0()) -> 0(),
  sum(s(x)) -> +(sqr(s(x)), sum(x)),
  sum(s(x)) -> +(*(s(x), s(x)), sum(x))}
 Comment:
  We consider a duplicating trs.
  FAIL:
   Open