Thank you for your information, very helpful. After my first post I got to thinking about "grouping signs" and decided they were needed to make AB an item, so no problem there.
The entire subject of "over" (and "under) is a lot clearer now but I still have a couple of questions and suggestion which I added to an attachment in order to show the simbraille.
I have a blind friend who is also studying UEB and she prefers my construction of a right arrow over as opposed to the example on p.72. (in attachment)