I have to figure out a question for my linear algebra course and ever since the beginning of the course, we've been using llvll or llull (v and u being vectors with a line over top of them) and I've been wrongly (I now know) assuming these are weird-looking absolute value signs. I've looked in my textbook but can't find what it means. (I've also tried Google with no luck). Could somebody please explain? Thank you so much!