This means that you can do anything UNLESS it:2. Unless otherwise stated, it is generally understood that if notes, resources, calculators, actions etc., are not excluded, then they are permitted unless they violate the spirit of the problem.
- 1. is specifically prohibited by the rules
2. violates the spirit of the competition
3. presents a safety hazard
4. provides an unfair advantage.
Interpreting rules is colored by an individuals knowledge and past experiences. It's common for rule-writers to understate what they want simply because they know what they mean to say. Others who have not had the same conversations/experiences can easily arrive at a completely different interpretation than what was intended.
Many problems are a result of language. Words have varied and often abstract meanings that can lead to misunderstanding. Often the insertion (or omission) of a comma can drastically change the meaning of a sentence.
I could go on to give several other examples of how the rules are interpreted differently, but the point is: The only sure way to know how the rules will be applied is to ask the person who will be interpreting them for YOUR competition.