> "Complicated" means here that the whole term is more than three pages
> long. Starting from a fraction with products of constants, values and
> variables in the numerator and denominator you subsitute some of the
> values in the numerator and the denominator by fractions with products
> of constants, values and variables, then you substitute some of the
> variables in all of the numerators and denominators by fractions
> with ... again and so on. Thus the only pattern of the form f is given
> is that there are only basic arithmetic operations in its definition.

> Of course, I could choose a set of numerical values for our constants
> and evaluate f in some points (this gives us float points) and get the
> coefficients by interpolation. But we are looking for a description of
> the coefficients as functions of some other variables, so numerical
> values for the coefficients don't help us.

> By the way, there is another question more elementary: How can I
> compute in \mathbb{C}(t) (i.e. the quotient field of the polynomial
> ring) using sage?