Some add also ο, as in ἐκεῖνο, τοῦτο, ἄλλο. The final elements of duals are three, α, ε, ω, as Ἀτρείδα, Ἕκτορε, φίλω; of plurals, four, ι, σ, α, η, as φίλοι, Ἕκτορες, βιβλία, βέλη.