When the -θη suffix is placed on a stem that ends in a final π or β, what happens?
becomes φ
When the -θη suffix is placed on a stem that ends in a final κ or γ, what happens?
becomes χ
When the -θη suffix is placed on a stem that ends in a final τ, δ, or θ, what happens?
becomes σ
When the -θη suffix is placed on a stem that ends in a final φ or χ, what happens?
remain unchanged