I have a problem which I do not understand why my solution doesn’t work.

Here is the setup: I integrate the function

```
func = Integrate((z*p),{z,0,1},{p,0,1}) = 1/4
```

However, now i want to replace

```
func=(z*p)/.z->dx*Exp(x*z1+y*p1)/.p->dy*Exp(x*z1+y*p1)
```

where dx, dy symbolises derivative of x and y, respectively. I change the name z->z1, p->p1 because mathematica cannot handle the replacement correctly but keep in mind that it is the same. Now by taking the derivative and the limit x -> 0 and y -> 0 you should get the original function back.

But before that, i want to integrate

```
eval=Integrate(func,{z1,0,1},{p1,0,1})
Limit(D(D(Coefficient(eval,dx*dy),y),x), {y->0,x->0}) = 1
```

So as you can see i get the wrong result and i do not know where the error is. It is very important that i take the derivative and limit after the integration step