I have the following double definite integral.

$ int _0 ^ { frac {d} {1-r}} int _ { frac {d + r x-x} {r}} ^ s [(1-r) x+r y -d]$ dydx

with the constraints: $ 0 leq d leq $ 1, $ 1 leq s leq $ 4, $ 0 leq r leq $ 1, $ 0 leq x leq s $, $ 0 leq y leq s $.

My code to solve this integration is

```
To integrate[(1 - r)*x + r*y - d, {x, 0, d/(1 - r)}, {y, (d + r*x - x)/r,s}]
```

And I had

```
(d 3 - 3 d 2 + 3 + 2) - (6 - 6)
```

But I think it's not correct because the variables $ x $ and $ y $ are linked by $ 0 and $ s $ and so I think I need additional constraints on the boundaries, that is to say

$ frac {d} {1-r} leqs $ and $ 0 leq frac {d + rx-x} {r} leq $.

And I wonder how to add these two constraints to solve the integration above. Can someone help you please? Thank you!