कृसृभृवृस्तुद्रुस्रुश्रुवो लिटि

The personal endings of the लिट् (Perfect Tense) do not get the augment इट् after 1 कृ 2. सृ 3. भृ 4. वृ 5. स्तु 6. द्रु 7. स्रु 8.श्रु।
Thus कृ - चकृव, चकृम; सृ, ससृव, ससृम; भृ, बभृव, बभृम; वृञ्, ववृव, ववृम; वृङ्, ववृवहे, ववृमहे; स्तु, तुष्टुव, तुष्टुम; द्रु, दुद्रुव, दुद्रम; स्रु; सुस्रुव, सुस्रुम; श्रु; शुश्रुव, शुश्रुम ॥ सिद्धे सत्यारम्भो नियमार्थः, क्रादय एव लिट्यनिटस्ततोन्ये सेट इति ॥

These roots with the exception of वृ are Anit by rule 7.2.10; their special mention here is for the sake of niyama, namely, these roots alone are Anit in the Perfect, other roots are all Set in the Perfect. Thus बिभिदिव, बिभिदिम, लुलुविव, लुलुविम ॥ All anudatta roots of the Dhatupatha are to be understood, by this rule, to get इट् ॥ The affix थ of the Perfect gets इट् after वृञ्, as the irregular form ववर्थ in 7.2.64, indicates that in the Veda, थ does not get इट् after वृञ्, but in the secular literature it does. By 7.2.63, the थ would have got इट् after स्तु, द्रु, स्रु and श्रु; that इट् is also prohibited by the present sutra. As तुष्टोथ, दुद्रोथ,
स्रुस्रोथ, शुश्रोथ ॥

Vart:- इट् is added when कृ takes the सुट् augment : as संचस्करिव, संचस्करिम ॥ The rule 7.2.63, applies here also, as संचस्करिथ ॥