History of the Greek alphabet retained the sound. A symbol based on the left-hand half ( ├ ) of the letter Η was therefore sometimes used to indicate the presence of where necessary, and its absence was indicated by a symbol based on the right half. During the classical period, ΕΙ came to be pronounced and ΟΥ came to be pronounced , Υ having meanwhile moved to . By about 200 BC, a system of diacritical marks was invented, representing the tone accents in use in Ancient Greek. This also helped to indicate the length of the vowels Α, Ι, and Υ in certain cases
Coptic alphabet accepted to separate it, with the proposal noting that Coptic is never written using modern Greek letter-forms (unlike German, which may be written with Fraktur or Roman Antiqua letter-forms), and that the Coptic letter-forms have closer mutual legibility with the Greek-based letters incorporated into the separately encoded Cyrillic alphabet than with the forms used in modern Greek. In Old Coptic, there were a large number of Demotic Egyptian characters, including some logograms. They were soon reduced to half a dozen, for sounds not covered by the Greek alphabet. The following letters remained: In Unicode, most Coptic letters formerly shared codepoints