To refute the predestinarian heresy Hincmar composed his De praedestinatione Dei et libero arbitrio, and against certain propositions advanced by Gottschalk on the Trinity he wrote a treatise called De una et non trina deitate.
Mahommed in fact represented a revolt against the anthropomorphism of commonplace Mahommedan orthodoxy, but he was a rigid predestinarian and a strict observer of the law.
His first encounter was with the heresiarch Gottschalk, whose predestinarian doctrines claimed to be modelled on those of St Augustine.