### How to define a differential or integral operator?

Hi,

What's the difference between the method notation and function notation? Is it possible to define a differential or integral operators using either of these notations or else?

I'm a beginner, just tried a bit codes like the followings

```
reset
var('x,a,b')
L='diff(x,a,b)'
f=function('f',x)
f.diff(x,a,b)
```

or

```
reset
```~~var('x,a,b')
L=[c='diff(x,a,b)'] ~~var('x,a,b,c')
L={c:'diff(x,a,b)'} # defining a dicionary
f=function('f',x)
f.L[c]

and codes like these
but none worked. Any idea?