# Is it possible to define (or assume) the derivative of a function

What i would like to do is define formal symbolic functions

`f1 = function('f1',latex_name = 'f_1')(x)`

and set their derivative or at least be able to substitute their derivative. As an example assume I defined f1,f2,f3,f4 then I would set dx f1 = f2+f3 and what I would expect is

```
f1.derivative(x)
```

to output

```
f2(x)+ f3(x)
```