Question: In what century did Olaf Geirstad-Alf  and Halfdan the Black live in?
Sentence (from "Olaf Geirstad-Alf"): Olaf Gudrødsson, or as he was named after his death Olaf Geirstad-Alf (Old Norse Ólaf Geirstaða Álfr), was a legendary Norwegian king of the House of Yngling from the "Ynglinga saga".
Relevant evidence: No