# differential form pullback

Hi All,

I have a differential form defined in 3D Cartesian Coordinates

$\mathit{{\sigma}}=\frac{x\mathit{dy}\mathit{dz}}{a}-\frac{y\mathit{dx}\mathit{dz}}{a}$

and the following map

$g:[{a}{\ast}\cos(\theta), {a}{\ast}\sin(\theta), z]$

How do I calculate the pullback $g^{\ast}(\theta,z)$ of $\sigma$ in SageMath

I've seen all the documentation of pullback in "manifold.pdf" but I am unable to apply those examples to my case.

Thanks.