How to determine that a lesson of a particular subject could only take place on a particular day. For example: Chemistry for 8th and 9th grades only on Wednesday.

It is set that 0 lessons can be on Monday, Tuesday, Thursday and Friday. So, chemistry can only be on Wednesday.

Similarly, it can be set that chemistry can take place only on other day (days) of a week – just left these days unchecked. Condition applies to checked periods (lessons).