3.3 Cover symbols for Phondex. A list of cover symbols aids the phondex rules in generating the various codes (normal, phonetic, dialect, compressed). The contents consist of two parts: unary symbols, digraphs. The convention is to specify vowels with the understanding that consonants are any other unary symbol. The two-letter sequences that need to be treated as single sounds (diphthongs or consonant clusters) are given in a second list. This makes it possible for the application of phondex rules to interpret the environmental conditions in their ANTE and POST portions.