> > +    >>> f = (-2*x - 2*x**2) / (3*x**2 - 6*x)
> > +    >>> apart_list(f)
> > +    (-1,
> 
> Is this always just 1 or -1?

Concluding from the examples I tried yes. But I do not
understand how this is computed, because it drops of the
`cancel` routine. (Which has no useful documentation at all.)
And I did not look into its source.