In sthā etc. up to sit exclusive -- upasargāt sunotisuvatisyatistautistobhatisthāsenaya sedhasicasañjasvañjām [[8.3.65]] to parinivibhyaḥ sevasitasayasivusahasuṭstusvañjām [[8.3.70]], this substitution of ṣ takes place then also, when the reduplicate intervenes and the sa of the reduplicate is also changed to ṣa,
The words प्राक् सितात् are understood here also. The स्यादि roots are, स्था, सेनय &c in 8.3.65 and ending with सेव् in 8.3.70. The sutra consists of two sentences : (1) The षत्व takes place in स्था &c. even when a reduplicate intervenes; (2) The स of the reduplicates of स्था &c. is changed to ष ॥ The first is a vidhi rule, and the second is a niyama rule.
Thus परितष्ठौ where the abhyasa त intervenes. This applies even to roots other than those which have been taught with a ष in the Dhatupatha. As अभिषिषेणयिषति, परिषिषेणयिषति (सेनया अभियातुमिच्छन्ति). This applies moreover to reduplicates which end in अ, as अभितष्ठौ; here the स् would not have been changed to ष (by 8.3.59) as it is not preceded by इ or उ ॥ Another raison d'etre of this sutra is that it prohibits षण् 8.3.61. As अभिषिषिक्षति, परिषिषिक्षति ॥
The word अभ्यासस्य is for the sake of niyama, as we have said above. स of स्था &c. and of no other roots is changed to ष ॥ As अभिसुसूषति from षू प्रेरणे with सन्, the augment is debarred by 7.2.12: the root स् is unchanged by the niyama prohibition of 8.3.61; the reduplicate स् remains unchanged by the restriction of the present sutra.,