Problems with duplicate abilities...

I am well aware that trying to use two versions of the same spell on a single unit can cause some problems, but I have some questions.

1. If there are two hero abilities based on the same original ability, can either of them be LEARNED properly?
2. If there are two hero abilities based on the same original ability, can either of them be USED properly?
3. If a unit has a hero ability, and the same type of ability (non-hero) which appears in a spellbook, will they both work properly? If not, then which, if either, will work properly?
4. If two of the same type of spell appear in the same spellbook ability, can they be used properly?

edit - I just found out, the two hero abilities will be learned fine, but I don't think they will be used normally. I remember something like this in an early version of Tides of Blood. I tested just now with passive abilities, the hero definatly learns them both normally but I don't think he uses them normally (they were both stat bonus, and one of them had the increases set to 0, so there is no way for me to know one way or the other).
That's all I need to know, since the skills in my map won't have any actual effect, the effects are applied in triggers once they are learned, so I can base them all off of one ability...

1) Yes. But if you learn the other one, it will do both effects.

2)Yes, same reason above, just you can't have both of the abilities learned.

3)I belive they should, they definitly will work if the spellbok was an item.

4)No, it just wouldn't work. Well it would, just it would do both of them at the same time.