How Not?

Aeschylus, Libation Bearers 122-123 (tr. Herbert Weir Smyth, slightly modified):

                              ELECTRA
And is this a righteous thing for me to ask of Heaven?
                              CHORUS
How not? To requite an enemy evil for evil?

                              ΗΛΕΚΤΡΑ
καὶ ταῦτά μοὔστιν εὐσεβῆ θεῶν πάρα;
                              ΧΟΡΟΣ
πῶς δ᾿ οὔ, τὸν ἐχθρόν γ᾿ ἀνταμείβεσθαι κακοῖς;

See also William Allan, "The Ethics of Retaliatory Violence in Athenian Tragedy," Mnemosyne 66.4/5 (2013) 593-615 (at 602-603).