Open NAP problems

There are open problems related to the non-aggression principle (NAP) which I would like to find answers to. If you are aware of a good answer to any of those, please let me know and I will be endlessly grateful. I will even buy you a drink if you want.

OK, so here are the seven big questions:

1. In what sense is NAP a 'principle'? What happens if you break it? What happens if you follow it?

2. In what situations (if any) is it worth to or ethical to breach NAP?

3. How to respond to people violating NAP?

4. What other ethical principles are natural extensions of NAP?

5. How to precisely define violence? Is violence just one thing or is it many different things?

6. How does NAP spread?

7. Is the state just one thing or is it many different things?