Iaith y dyffryn : arolwg o'r Gymraeg ymysg rhieni a disgyblion Dyffryn Tywi = Welsh in the Vale : a survey of the Welsh language among parents and pupils of the Tywi Valley by Heini Gruffudd. Published by Bwrdd yr Iaith Gymraeg in 2002. Publication and catalogue information, links to buy online and reader comments.