Full and divided lessons from one subject

In case, that a subject in the class is taught as a combination of lessons for entire class and for groups also, it is undesirable that lessons for groups to be separated with lessons for full class. It would meant, that one group will be forefront of teaching as a second group.

Let's take an example, when Chemistry lessons are taught as "theory and laboratory practices". Laboratory practices are set as double lessons and students in the class are divided into two groups. For assuring that laboratory lessons for both groups will follow and not be at the same day as a full class' lessons, use this relation: