It would be good if when reusing a topic (Topic A), users were told what other topics Topic A refers to in other existing books. This would help users identify what topics might be suitable for Topic A to refer to in their own book.

For example, for a given topic, the user might be told:

"Existing relationships to other topics:

  Prerequisite:
    Topic B
  Refer-to:
    Topic C
    Topic D"

I'm not sure what headings would be best. For example, "Refer-to" or "See Also".