Task: Sentence Expansion
Input (English): In the " Prose Edda " book " Gylfaginning " , Elli defeats Thor in a wrestling match .
Output (English): In Norse mythology ( a subset of Germanic mythology ) , Elli ( Old Norse " old age " ) is a personification of old age who , in the " Prose Edda " book " Gylfaginning " , defeats Thor in a wrestling match .