> >The Pad. should make
> >explicit mention of the preverb if there is one.
>
> But there isn't one in the Pad. form <ayunak>!
Exactly. The point is: Since the Padapatha mentions no preverb with
this form, it doesn't have any. This is confirmed by the lack of
accent. That rules out a preverb /a:-/, leaving only a lengthened
augment as a viable interpretation.