The idiomatic way to check if a list contains something in Groovy is to use `in`.

```
if ('b' in ['a', 'b', 'c'])

```

But how do you nicely check if something is not in a collection?

```
if (!('g' in ['a', 'b', 'c']))

```

Using logical not seems messy and the `!` is hidden to the casual glance. Is there a more idiomatic way to do this in Groovy?

Thanks!