Hi community.

My problem is *simple*, but I don't know if there is a solution implemented in `cadabra`

.

I have expressions, after applying the `substitute`

algorithm, that contain higher order partial derivatives, say

`\partial_{t i}{ T^{j} }`

or

`\partial_{t i j}{ T^{j} }`

or

`\partial_{t i t j}{ T^{k} }`

I'd like to rewrite any possible combination of partial derivatives in a sorted way, with all the "time" derivatives at last, i.e. to transfor the above expressions to:

```
\partial_{i t}{ T^{j} }
\partial_{i j t}{ T^{j} }
\partial_{i j t t}{ T^{k} }
```

respectively.

## Question

Does anyone know how to achieve this? Considering that it might be an undefined number of "time" and "space" derivatives.