# How do I code a Laurent Series with variable coefficients?

Edit: Adding more context.

I am attempting the following procedure:

- Begin with a polynomial $Z(u)$ with variable coefficients, of the form $1 + a
*u + b*u^2 + c*u^3 + p*b*u^4 + p^2*a*u^5 + p^3*u^6$. - Examine the coefficients of $Z'(u)/Z(u)$ as a power series in $u$.

It is this quest which leads me to attempt to construct a LaurentSeriesRing with variable coefficients. However, I keep encountering TypeErrors, I am wondering if a kind soul could help me in my quest. I will use here a very simple polynomial f to get the point across.

I am attempting to construct a LaurentSeriesRing with variable coefficients. However, I keep encountering TypeErrors, I am wondering if a kind soul could help me in my quest. I will use here a very simple polynomial f to get the point across.

```
sage: R.<t> = LaurentSeriesRing(QQ, 't')
sage: var('a')
a
sage: f = 1 + a*t
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-31-06d3f2f41e45> in <module>()
----> 1 f = Integer(1) + a*t
sage/structure/element.pyx in sage.structure.element.Element.__mul__ (/usr/lib/sagemath//src/build/cythonized/sage/structure/element.c:12443)()
sage/structure/coerce.pyx in sage.structure.coerce.CoercionModel_cache_maps.bin_op (/usr/lib/sagemath//src/build/cythonized/sage/structure/coerce.c:10496)()
TypeError: unsupported operand parent(s) for '*': 'Symbolic Ring' and 'Laurent Series Ring in t over Rational Field'
```

I also tried:

```
sage: R.<u> = QQ[]
sage: var('a')
a
sage: f = 1 + a*u
sage: ff = derivative(f, u)
sage: R.<u> = LaurentSeriesRing(QQ); R
sage: f/ff + O(u^5)
----------------------
TypeError Traceback (most recent call last)
<ipython-input-28-c4846de7ced8> in <module>()
----> 1 f/ff + O(u**Integer(5))
sage/structure/element.pyx in sage.structure.element.Element.__add__ (/usr/lib/sagemath//src/build/cythonized/sage/structure/element.c:11198)()
sage/structure/coerce.pyx in sage.structure.coerce.CoercionModel_cache_maps.bin_op (/usr/lib/sagemath//src/build/cythonized/sage/structure/coerce.c:10496)()
TypeError: unsupported operand parent(s) for '+': 'Symbolic Ring' and 'Laurent Series Ring in u over Rational Field'
```