Hello everyone!

In my computations I need to define some arbitrary field function, for example F, which dependes on field of my theory p(x). I tryed to define p like a coordinate and then set that pi depends on all other coordinates, as follows:

```
{t, x, y, p}::Coordinate.
p::Depends(t,x,y).
K::Depends(t,x,y, p).
```

But then I take the derivative with respect to p, I am getting a vector index so it doesn't work for me. I've tryed to define some 'special' derivative for p, but this interferes with further calculations in components. I also tryed to write something like

```
map_sympy(F, 'Function("F")(p))
```

but it didn't work. It seems to me that I don't see some very simple option.