1. What is the origin of -au in Sanskrit dvau and the classical Sanskrit dual nom. and acc. -au? Is there any sort of "dualizing" or "binary/bipolar" particle *u or the like? Such as in *we(:) (*u + *e(:)?) "or" or Gothic thau, jau ( tha-u, ja-u?)?
2. Why did the IE dual have the same form for nominative and accusative? (I realize this is probably unanswerable.)
3. Is there any evidence at all for an ablative plural/dual ending in Proto-IE? Was it always identical to the dative plural/dual? Does this state of affairs not lead to confusion?
4. Are the Avestan ablative singular endings -oith/-aedha (i-stems), -aoth/-wath (u-stems), -aya:th (a:-stems) an innovation or inherited? th stands for thorn or theta.
Hoping for answers,
Andrew Jarrette