How to ensure lunch break for teachers

If you need to make sure that every teacher has at least one period free during lunch time for lunch, you can input it this way:

Example: Lunch between periods 3-5. This means there are 3 periods available. So we can input it making sure that during 3.-5. period teacher can have max 2 lessons.

Go to menu - Specification - Relations - Advanced and input values according to this picture: