Teacher cannot teach 4th in Grade 5 and 5th lessons in Grade 6

This constraint can be usefull if you have a situation that you have different bells in grade 5 and grade 6th.

You need to use cardrelationship:

See also:
We have different recess times in parts of school. How to input it? (Solution1)

We have different recess times in parts of school. How to input it? (Solution 2)