(VAR x) (RULES top(free(x)) -> top(check(new(x))) 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) )