The monograph reflects the current standard of knowledge about the open questions considered, taking care to collect and collate all the revelant ideas, facts and formulae which have been until now widely scattered throughout the literature. For the first time, these aspects are collated in book form. Care is taken to clarify the issues, give a systematic collection of conditions which prospective solutions of these open questions have to meet, and gather and collate various useful theoretical concepts and results.

The monograph reflects the current standard of knowledge about the open questions considered, taking care to collect and collate all the revelant ideas, facts and formulae which have been until now widely scattered throughout the literature. For the first time, these aspects are collated in book form. Care is taken to clarify the issues, give a systematic collection of conditions which prospective solutions of these open questions have to meet, and gather and collate various useful theoretical concepts and results.