# Polynomials over number fields

Below I define a polynomial ring K[s,t]. My goal is to compute the minors of a large matrix with entries in this ring.

```
var('x')
# K.<t> = NumberField(x^2-2)
K.<s,t> = NumberField([x^2-2,x^2-5])
R.<p0,p1,p2,p3,p4,p5> = K[]
M = Mat(R,10,10).random_element()
mins = M.minors(2)
```

This code works fine, but if I replace the last line with

```
mins = M.minors(7)
```

it fails with the error message

```
TypeError: no conversion to a Singular ring defined
```

Is it possible to avoid this error?