### Equation with sign function

Hi all,

I have the following piece of code

```
f(x) = 2*unit_step(x)
u = function('u')(x)
eqn = diff(u,x) + u == f(x)
v = desolve(eqn, u,ics=[0,0])
solve(v,x)
```

which gives me as `[x == 0, sgn(x) == -1]`

as solutions to the last equation. Could you help me find a way for Sage not to stop at `sgn(x) == -1`

?

Thanks