For anyone who wishes to pursue the complicated lives and multiple incarnations of this saint, Bernard Tanguy has written a most useful article, "Hagionomastique et histoire: Pabu Tugdual alias Tudi et les origines du diocese de Cornouaille" in Bulletin de la Societe archeologique du Finistere 115 (1986), pp. 117-142. He has also done a lot of work on place-name elements such as `Llan' (as has Oliver Padel). Karen Jankulak