How do I prevent duplicates, in XSL?

Question

How do I prevent duplicate entries into a list, and then ideally, sort that list? What I\'m doing, is when information at one level is missing, taking the information from

Answer 1

A truly XSLT 2.0 solution, also quite short:

Do note:

1. The use of types avoids the need to specify the data-type in .

2. The use of the separator attribute of