The Barddas of Iolo Morganwg, Vol. I., ed. by J. Williams Ab Ithel, , at sacred-texts.com
There are three benefits to be had from Cythraul: the defection of evil; a view to goodness; and the triumph of victory over what is contrary to the beneficial.
213:2 p. 212 Bardism recognises another principle of evil, which is called "DERA," respecting which Iolo Morganwg has the following note:--"The old Bardic idea was that the DERA usurped the occupation of Cylch y Ceugant, and that he would suffer none but himself to occupy it, destroying all other beings;--that God, being more powerful, is able to dispossess him, and, with Himself to occupy it, creates beings highly susceptible of happiness, to enjoy it with Him to all p. 213 eternity, on condition of joining with Him to resist evil. The common proverb is hence derived--'Myn y diawl y cwbl iddo ei hunan, fal y cybydd: mae Duw, fal yr haul, yn rhoi than i bob un arall.'"