# Problem with factor and imag.

I'm new to SageMath, and I'm not sure what's going wrong.

Here are the commands I enter and results I get:

```
sage: a, b, z = var('a, b, z')
sage: P = a*x - b*x
sage: Q = a*imag(z) - b*imag(z)
sage: P.factor()
(a - b)*x
sage: Q.factor()
0
```

Why is `Q`

factoring to `0`

?

Weird.

`assume(z, 'complex')`

seems to help.Also

Possible serious bug. Advice requested on

`sage-devel`

.