> Do you mean
> "Szemerényi" length in the nom.sg.? It is not compensatory, strictly
> speaking, since the vowel is lengthened also when no segments are lost,
> as in *dje:us.
It is said that what was lost here is "non-segmental phoneme" - syllabicity
of the following syllable; but popularly speaking,
I suppose that it could be described either as
the compensation for the loss of the final reduced vowel,
or maybe as metathesis and contraction:
nom. dejéweze > djéwz& ( > djé&wz) > djé:wz > djé:ws
acc. dejéweme > djéwm& > djéwm.
gen. dejewèse > d&jwès > diwós
nom. peh2etéreze > p&h2térz& ( > ph2.té&rz) > ph2.té:rz > ph2.té:r
acc. peh2etéreme > p&h2térm& > ph2.térm.
First the odd unstressed vowels were lost and the even ones reduced,
then the shwas next to H or R gave them their syllabicity,
whereas the remaining shwas transfered their mora to the preceding syllable.
P.A.