F. Chapoton recently wrote a program the behaviour of which I do not understand.

```
def fermat(n):
q = polygen(ZZ, 'q')
return sum(n ** j * binomial(n, j) * (-1) ** (i + n + j) *
binomial(n - 2 - j + 1, i + 1) * q ** i
for j in range(n - 1)
for i in range(n - 1 - j))
```

Now consider:

```
v = fermat(5)
print v.parent()
print v.list()
```

This outputs

```
Univariate Polynomial Ring in q over Integer Ring
[821, 181, 21, 1]
```

which is fine. However the loop

```
for n in (1..9):
v = fermat(n)
print v.parent()
print v.list()
```

gives the errors:

```
AttributeError: 'int' object has no attribute 'parent'
AttributeError: 'int' object has no attribute 'list'
```

What happens here?