Epsilon (uppercase ?, lowercase ?) is the fifth letter of the Greek alphabet, corresponding phonetically to a close-mid front unrounded vowel /e/. In the system of Greek numerals it has a value of 5. It was derived from the Phoenician letter He . Letters that arose from Epsilon include the Roman E and Cyrillic Ye. "Epsilon" (, "simple e") was coined to distinguish the letter from ??, which by the medieval period was pronounced the same way. The standard symbol for lowercase epsilon is the lunate epsilon ? (epsilon in MathML), which has its origins in Medieval Greek. In mathematical notation, the minuscule open e symbol ? (varepsilon in MathML) from the extended Latin alphabet is often used interchangeably with the lunate epsilon. The lunate epsilon ? is not to be confused with the set symbol ? or fal