Corpus of Electronic Texts Edition
The Wooing of Emer by Cú Chulainn (Author: [unknown])

paragraph 48

‘Of the daughters of Tethra's nephew, viz., Forgall the Wily is the nephew of Tethra, king of the Fomori, viz., the son of his sister, for nia and a sister's son is the same, and a champion is also called nia.’