I have troubles substituting functions when I have symbolic derivatives and I need to substitute more symbolic derivatives in my expression. Take for example

```
D[f[x, y], {x, 2}];
% /. f[x, y] -> x^2 h[x, y]

```

The output is

```
(f^(2,0))[x,y]

```

and not $x^2\, \partial\_x^{\,2}h(x,y)+4\,\partial\_x h(x,y) x + 2\, h(x,y)$.

While I've read that this happens because

```
D[f[x, y], {x, 2}] // FullForm

```

gives

```
Derivative[2, 0][f][x, y]

```

and `f[x, y]` is not present here anymore, I couldn't find a solution for this.

Any ideas?