The process of itacism, which resulted in the eventual identification of the sounds originally represented by ι, ει, η, ηι, οι, υ, and υι in /i/, was well advanced in Egypt by the beginning of the Roman period. ει and ι are alternate representations of /i/; η and ηι are identified; οι, υ, and υι all represent /y/. Moreover, there is a very frequent interchange of η with ι and ει, indicating that η also represented /i/ at least in the speech of many writers. On the other hand, there is a frequent interchange of η with ε (and sometimes with its phonetic equivalent αι) throughout the Roman and Byzantine periods, in similar documents and sometimes in identical phonetic conditions and even in the same words in which an interchange of η with ι or ει is found. There is also an occasional interchange of ε (αι) with ι and ει. (Gignac, Francis T (1975) A Grammar Of The Greek Papyri Of The Roman & Byzantine Periods – Volume 1 – Phonology (1975), page 235)