Vowel Assimilation

If 2 vowels meet and they are different (e.g. a-é) in compounds, the first one becomes short (except if it is ë) and the second one becomes long if it isn't already. (a-é to áe)

If 2 vowels meet and they are the same (e.g. w-w) in compounds, the first one becomes short and the second one becomes ë (w-w to ẃë)