Abstract
This book consists of two parts: a reproduction of the author's unpublished Lecture Notes (1968-69), and his Author's Notes (2008). The former starts with three main conjectural relationships and gives various approaches towards their proofs. Though they remained formally unpublished, these Lecture Notes circulated widely and have stimulated research in various directions. The main conjectures themselves have been proved since then. The Author's Notes (2008) give detailed explanations of these developments, together with open problems.