Addasiad o = Adaptation of: Planed Mewn Perygl (Ehangu Gorwelion), Cyhoeddiadau Cyngor Cwricwlwm Cymru, 1991.
Planed mewn perygl. ISBN 1857870980. Published by Canolfan Astudiaethau Iaith in 1994. Publication and catalogue information, links to buy online and reader comments.