PIE ablaut

From: Alexander Dakhov AKA Dusty
Message: 2621
Date: 2000-06-09

Dear members of Cybalist!
Can anybody help me and tell <b>strict<\b> and <b>exact<\b>
definition of Proto-Indo-European ablaut? Especially:
a) Does it count 2 (e/o) or 3 (nil/e/o) grade?
b) Does any other vovels (except e/o) are involved?
c) How PIE ablaut connect to morphology? Which grade are used in
nouns or in verbs?

WBR, Alexander Dakhov.