This is the 6288th most frequent Russian word.
упомянутых
"Mentioned."
Here, 'упомянутых' describes 'книг' (books) as those that have been referred to earlier or mentioned.
Из всех упомянутых книг, эта оказалась самой интересной.
Out of all mentioned books, this one turned out to be the most interesting.
In this context, 'упомянутых' characterizes 'примеров' (examples) as those that were brought up or mentioned in a prior discussion.
Тема упомянутых примеров оказалась важной для обсуждения.
The topic of the mentioned examples turned out to be important for the discussion.
In this sentence, 'упомянутые' functions as an adjective derived from the participle 'упомянуть', describing 'пункты' (points) as those that were mentioned.