# Best way to really simplify ugly formulas

As a casual user of sagemath I am always struggling to get my formulas simplified:

```
var('rg rs r');
dens = 1-r^2*rs/rg^3;
idens = 1-rs/rg;
ism = 1/4 *(3*sqrt(idens)-sqrt(dens))^2 * dens;
d = derivative(ism, r);
d.simplify_full();
```

The result has some potential for simplification, at least in terms of what think simplification might be. Can someone provide some hints as to how to get better results than from `simplify_full()`

?