There are no attestations of Sjöfn in the Poetic Edda.
Chapter 35(p.30): Lofn is listed eighth among the Asyniur. She is so kind that she can get permission from Odin or Frigg for the union of men and women, even when it was previously forbidden. The word for permission, lof, is said to derive from her name.
Eighth Lofn: she is so kind and good to pray to that she gets leave from All-father or Frigg for people’s union, between women and men, even if before it was forbidden or refused. Hence it is from her name that it is called lof [permission], as well as when something is praised (lofat) greatly by people.
Chapter 75(p.157): Lofn is named in a systematic list of the Asyniur.
Now shall all the Asyniur be named. Frigg and Freyia, Fulla and Snotra, Gerd and Gefiun, Gna, Lofn, Skadi, Iord and Idunn, Ilm, Bil, Niorun.
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