The logic was based on a billing app I created that utilized the method outlined in the below link to make sure that previously selected choices have been eliminated:
X is not static. It represents the Relationship outlined in the above link that keeps track of the selected choices. Every time a choice is selected, Relationship value is incremented by 1, and the number of choices reduced. I hope that makes it cleared.
Thanks for your help on this, @ThinhDinh.