> So far as I know, the equation is simplicity itself: PIE *e, *a, *o > AI
> <a>; PIE *e:, *a:, *o > AI <a:>.
Not that simple.
PIE *a > AI <a>
PIE *e > AI <a> with palatalisation of certain preceding consonants
PIE *o > AI <a> in a closed syllable,
> AI <a:> in many open syllables (all, where there was e/o
ablaut)
This means AI shows the PIE distinction of e/a/o in the same places as
Greek, Latin, Germanic, etc., and that ablaut is just as certain within AI
as elsewhere.
Peter