Hittite spelling

[Peter &/or Graham]

>Hittite spelling ... distinguish[es] (in medial position at least)
>C from CC, where usually the single consonant etymologically
>derives from a PIE voiced one and the geminate from a PIE
>voiceless consonant.

What is actually the state of play with this?   It began as a hypothesis,
with some evidence in its favour, and some against.   Is it turning into one
of those things that everyone agrees on because it's tidy, or is the
emerging agreement soundly based?

Peter