Polish Rational

Master (a28e678):
```
$ ./expand2
Expanding: ((y + x + z + w)^15 + w)*(y + x + z + w)^15
1539ms
number of terms: 6272
$ ./expand2
Expanding: ((y + x + z + w)^15 + w)*(y + x + z + w)^15
1534ms
number of terms: 6272
```