# desolve not using/understanding assume()

I am trying to solve a differential equation with symbolic variables, but assume() does not seem to help answer maximas question:

```
t,a,b = var('t,a,b')
v = function('v',t)
de = diff(v,t)-a*v^2-b
assume((a*b)>0)
sol=desolve(de, dvar=v, ivar=t)
```

I still get the error message:

```
TypeError: ECL says: Maxima asks: Is a*b positive or negative?
```

How can i fix this?