I do not intend to make further changes to this document. However, if you do find any inaccuracies or errors that must be corrected in order for things to make sense, please let me know and I will make a new revision with appropriate changes. And I am always happy to answer questions in order to clarify your understanding. Unfortunately, this is not a very trivial topic and the document cannot fit a lot of the required context information. There are several links to references which contain further details about some aspects, and these are all worth reading for additional background information. In any case, please ask me to clarify when in doubt.