Answers

1. Some authors enters "GDH" (abreviation for glutamate dehydrogense).

The boolean "OR" returns the files containing this keyword.

2. On the other hand, some files containing "GDH" are not related to glutamate dehydrogenase.

For example, GDH can mean also GLUCOSE dehydrogenase.

Therefore, the files containing one or several of the keywords of the list are eliminated using the boolean "NOT".