Rachel Bromwich, Trioedd Ynys Prydein, pp. 138–145. This is the only triad which draws its content entirely from Geoffrey. References to the Welsh Triads use Bromwich's numbering; Bromwich's 51 forms part of #5 from the Red Book of Hergest.
Bromwich, Trioedd Ynys Prydein, pp. 103 – 104. Hergest Triad 50.
Bromwich, Trioedd Ynys Prydein, pp. 168 – 170. Hergest Triad 21.