Preemption checking is making sure no one else has written a paper or article that is substantially similar to your proposed paper. Preemption is fairly subjective and is more important if you are working on publishing with a journal. However, it is important to still make this review with your seminar paper.
A published work or article may be substantially similar to your paper if multiple factors below are the same:
Conduct searches for articles and/or book chapters in:
TIP: Keep track of articles and book chapters you find that are about the same subject. If they don't preempt your work, they may serve as helpful research for your paper.
All is not lost! Consider this:
Learn More with Preemption Checking CALI lesson: http://www.cali.org/lesson/8989