# How to express (-t^2 + x^2 + y^2 + z^2) as (x_μ)^2 ?

Hi Manifolds experts

I'm a newbie to Sage Manifolds; I find it fascinating, thanks! I have searched for the answer in the forum and documentation but so far without success.

In the code below, I wrote out `x^2`

in full as `-t^2 + x^2 + y^2 + z^2`

. Is there a way to write it as something like `x^2`

or `g[_μν] x[^μ] x[^ν]`

? I tried but couldn't find how and got syntax errors.

Also: is there a way to make the output show the denominator as something like `x^2`

or `g[_μν] x[^μ] x[^ν]`

?

Here is my code:

```
from sage.all import *
%display latex
M = Manifold(4, 'M', latex_name=r'\mathcal{M}', structure='Lorentzian')
X.<t,x,y,z> = M.chart()
F = M.scalar_field(1/(-t^2 + x^2 + y^2 + z^2))
dF = diff(F)
dF.apply_map(factor)
display(dF.display())
```

I am using SageMath version 9.5, Release Date: 2022-01-30. My OS is Ubuntu 22.04 (itself on WSL2 on Windows 11 latest).

Thank you GPN