De E apud Delphos

Περὶ τοῦ Ε τοῦ ἐν Δελφοῖς Plutarch. Plutarchi Chaeronensis Moralia, Vol 3. Vernardakēs, Grēgorios N., editor. Leipzig: Teubner, 1891.

Of the word ΕΙ engraven over the gate of Apollo's temple at Delphi (eng) Plutarch. Plutarch's Morals, Vol. 4. Goodwin, William W., editor; Kippax, R, translator. Boston: Little, Brown, and Company; Cambridge: Press of John Wilson and Son, 1874. The Ε at Delphi (eng) Plutarch. Moralia, Vol. 5. Babbitt, Frank Cole, translator. Cambridge, MA: Harvard University Press; London: William Heinemann Ltd., 1936 (printing).