Here are the references I promised to
Miguel some time ago (on PIE o-presents and related stuff).
Jasanoff, Jay H. 1979. "The position of
the hi-conjugation". In Wolfgang Meid and Erich Neu (eds.), Hethithisch und
Indogermanisch. Innsbruck: Innsbrucker Beiträge zur Sprachwissenschaft, pp.
79-90.
-- 1992. "The role of o-grade in Hittite
and Tocharian verb inflection". In Edgar C. Polomé and Werner Winter (eds.),
Reconstructing Languages an Cultures. Berlin/New York: Mouton de Gruyter, pp.
129-156.
Jasanoff is currently working on a new
book, _The hi-Conjugation in Hittite and Indo-European_, which will analyse in
detail the relationship between the Hittite verbal system and those of
the other IE languages.
Piotr