इड् अत्त्य्-अर्ति-व्ययतीनाम्

As आदिथ, आरिथ and संविव्ययिथ ॥ The root व्येञ् is not changed to व्या 6.1.46 in the Perfect. By 7.2.63, the roots अद् and व्य would have optionally been सेट्, and ऋ never, therefore, the present sutra makes the इट् augment compulsory. The इट् is repeated in the aphorism for the sake of clearness, the rule could have stood without it, for the anuvritti of 'optionally' could not have run into it from the last sutra: for if it was an optional sutra, the enumeration of अद् and व्य was useless, as they were already provided for by 7.2.63. Therefore, this sutra makes an invariable rule.,