Read this: The evolution of Proto-Greek should be considered within the context of an early Paleo-Balkan sprachbund that makes it difficult to delineate exact boundaries between individual languages. The characteristically Greek representation of word-initial laryngeals by prothetic vowels is shared, for one, by the Armenian language, which also seems to share some other phonological and morphological peculiarities of Greek; this has led some linguists to propose a hypothetical closer relationship between Greek and Armenian, although evidence remains scant.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): What is uncommonly seen in the Greek language that is not a constant ?
unanswerable