(VAR x y)
(RULES
  top1(free(x),y) -> top2(check(new(x)),y)
  top1(free(x),y) -> top2(new(x),check(y))
  top1(free(x),y) -> top2(check(x),new(y))
  top1(free(x),y) -> top2(x,check(new(y)))
  top2(x,free(y)) -> top1(check(new(x)),y)
  top2(x,free(y)) -> top1(new(x),check(y))
  top2(x,free(y)) -> top1(check(x),new(y))
  top2(x,free(y)) -> top1(x,check(new(y)))
  new(free(x)) -> free(new(x))
  old(free(x)) -> free(old(x))
  new(serve) -> free(serve)
  old(serve) -> free(serve)
  check(free(x)) -> free(check(x))
  check(new(x)) -> new(check(x))
  check(old(x)) -> old(check(x))
  check(old(x)) -> old(x) 
)