*hes- "to be"

Here's another verb question. If you're getting tired of all my questions
about PIE morphology, can anyone recommend a good book with it all in (in
English or French, please, my attempts at the Slavic languages have so far
been unsuccessful!)?

I've been told that *hes- "to be" was by nature an imperfective stem. How
then were the perfective and aorist stems formed for this verb? Was it
irregular in PIE (like it is all of PIE's descendants) and if so, how? I
know it was an athematic verb, hence the athematic endings like *hesmi "I
am".

Oh, and did it have a mediopassive form and if so, what was it used for.

hes-si ne hs-si-we?

Dan

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Lo deu nu preca êl'aisún necoui. God prays at noone's altar.

Dan Jones: www.geocities.com/yl_ruil/
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