Arg. Saesneg gwreiddiol = Original English ed.:Aberystwyth:Centre for Educational Studies,1993.
Trafod data. Llyfr 1, Tebygolrwydd by I. Gwyn Evans. ISBN 1856442195. Published by Canolfan Astudiaethau Addysg in 1993. Publication and catalogue information, links to buy online and reader comments.