set criteria on check boxes

set criteria on check boxes

Hello

I have a check box set with 3 entries:

1. M.,
2. Mms.
3. Unknown

the criteria contains work well

The criteria not contains is not working:
If I select not contains "unknow", it will return all the records that has at least M. or Mms.

How can I search for all the records that DON'T have Unknow selected?

Thanks

e.chataigne