Easy ways in One aid to taking in information is first to go through following a substructure and let the rest take care of itself (a surprising amount of the rest gets tacked on). To facilitate this, each description of a part is followed by a quick trip through that part, which the reader may care to follow. If it is true that one picture is worth a thousand words then an easy but fruitful way into this book is to browse through selected pictures, and overleaf is a table of possibilities. One might take every second or third entry, for example.