“…It was, and is, the purpose of this paper to give an adequate, though by no means complete answer to this question. This project, however, has to bear in mind that a lot of detailed information is available in a series of recent papers and preprintswhich I realised only in the winter of 2005 ( [2], [3], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [26]), due to R. Devaney and collaborators, so that the picture to be drawn here has to be complementary to the picture drawn in the above papers; certain overlaps, however, are unavoidable.…”