By GaC he means "Genealogies from the work generally known as "Hanes Gruffudd ap...

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By GaC he means "Genealogies from the work generally known as "Hanes Gruffudd ap Cynan." (actually titled "Historia hen Gruffud vab Kenan vab Iago"), of which the earliest manuscript is Peniarth MS. 17 (mid-13th century), in "Early Welsh Genealogical Tracts", edited by P. C. Bartrum (University of Wales Press, Cardiff, 1966; pages 35-37.

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