CELT is indebted to Professor Aoibheann Nic Dhonnchadha, Dublin Institute for Advanced Studies, Dublin, who first suggested to make an electronic edition of this tract available, for kindly giving of her time and assistance in this work, and for examining the manuscripts to resolve some uncertainties in the variant readings. CELT is also indebted to John A. Williams, M. Phil., University of Sydney, for his kind permission to use the revised translation published in his Thesis, and for supplying valuable bibliographical references, and to Dr Daniel Mc Carthy, Trinity College Dublin, for comparing the translations, for making helpful comments on the text and diagrams, and for supplying valuable bibliographical references.