Proto-Indo-European mythology realm of Midgard. Other dragon-slaying myths are also found in the Germanic tradition. In the "Völsunga saga", Sigurd slays the dragon Fafnir and, in "Beowulf", the eponymous hero slays a different dragon. Reflexes of the Proto-Indo-European dragon-slaying myth are found throughout other branches of the language family as well. In Zoroastrianism and Persian mythology, Fereydun, and later Garshasp, slays Zahhak. In Slavic mythology, Perun, the god of storms, slays Veles and Dobrynya Nikitich slays the three-headed dragon Zmey. In Armenian mythology, the god Vahagn slays the dragon Vishap. In Romanian folklore, Făt-Frumos slays the fire-spitting monster Zmeu. In Celtic mythology,
Investigations into Germanic Mythology there is no explicit revelation in the poem Hárbardsljóð concerning the identity of the title figure, Harbard, who is concealed under this name remained disputed until the end of the 19th century. In the third volume of the same work, Rydberg's theory regarding the World Mill is discussed in relationship to the eddic poem Grottosöngr. He has also been mentioned as one of several writers who proposed analogs for Askr and Embla from comparative mythology, and who sought Indo-Iranian analogs for the Eddic Poem, Völuspá. In 2004, Swedish Doktorand (PhD student) Anna Lindén reviewed the full two-volume work on mythology,