Zeb wrote:

>Hi
> With compounds, is it always the cast that a+a=aa or can a+a
>sometimes = a

In lopasandhi (combining with elision) it is possible that a + a = a.

satta + ahaani = sattahaaha.m (for a week)
raaga + aggi = raagaggi (fire of lust)

In such cases the old grammars would not say that the two a's had combined
into one, but that the first had been elided ('dropped' if you will). In
other words, it is the same kind of sandhi as:

pa~n~naa + indriya.m = pa~n~nindriya.m

Best wishes,

Robert