Philologist Haukur Thorgeirsson points out that the four manuscripts of "Gylfaginning" vary in their descriptions of the family relations between Nótt, Jörð, Dagr, and Dellingr. In other words, depending on the manuscript, either Jörð or Nótt is the mother of Dagr and partner of Dellingr. Haukur details that "the oldest manuscript, U, offers a version where Jǫrð is the wife of Dellingr and the mother of Dagr while the other manuscripts, R, W and T, cast Nótt in the role of Dellingr's wife and Dagr's mother", and argues that "the version in U came about accidentally when the writer of U or its antecedent shortened a text similar to that in RWT. The results of this accident made their way into the Icelandic poetic tradition".