fix forgotten "<="
allow only adding to and removing a *non-root* leaf
unify all interval notation to {p,...,q}; fix \dots

- Many places still used [\depth{k}] and similar. Now it's \natInt{p}{q}.
- Use \dotsc or \dotsb everywhere (no other dots). For reasons/reference see
	http://en.wikibooks.org/wiki/LaTeX/Mathematics#Dots