Of a reduplicate, the hard compound (aspirate and un-aspirate) when preceded by a sibilant, are only retained, the other consonants are elided.,
As चुश्च्योतिषति, from schyutir ksharane, तिष्ठासति, पिस्पन्दिषते ॥ Why do we say 'when preceded by a sibilant'? Observe पपाच ॥ Why do we say hard consonants? Observe सस्रौ ॥
Vart:- It should be said rather, a hard consonant preceded by a hard consonant or a sibilant is only retained : and the खर् consonants are elided : as in उचिच्छिषति, here उछ् becomes उच्छ् by the augment त् (तुक्); in the reduplicate the च् should be elided, and छ् retained out of च्छ; and not च् retained and छ् elided; for the च् represents त्, and if this were retained, it would be त् and not च् that would be heard : for by 8.2.1, the change of त् to च् is asiddha for the purposes of this rule.,