King’s College 2004 v Mistress Gunnvör sílfrahárr
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Bynames of Relationship : Grandparent Names
*Occasionally a person will be identified not only with a patronymic, but the grandfather will also be identified in the name. In such a case, the name of the grandfather occurs in the genitive (possessive) form, but the suffix meaning “son” also is in the genitive case, appearing as –sonar.
vÞórfinnr Sigurðar son Þórsteins sonar
(Thorfinnr, son of Sigurðr, who was Thorsteinn’s son)
(See http://www.s-gabriel.org/1990)
vTwo of the settlers of Iceland were identified in later writings as Þórvalldr Asvalldz son, "Thorvalldr Asvalldr's son," and Olver en hviti son Osvallz Auxna-Þóris sonar, "Olver the White, son of Osvaldr Auxna-Thorir's son".
(See http://www.s-gabriel.org/2743)
vThere are also examples of men identified as the grandsons of their grandfathers, e.g. Hrilfi son Ásgeirs Bjarnar sonar, "Hrilfli, son of Asgeirr Bjorn's son"...  Note that in this case, the father's entire name and byname are in the genitive (possessive) case.
(See http://www.s-gabriel.org/2516)