is is substituted for the root-vowel of 1. mī 2. mā 3. dhā (ghu) 4. rabh 5. labh 6. śak 7. pat 8. pad and 9. dā when the Desiderative san follows beginning with s (i.e. not taking the augment i) follows.,
The मी includes मीनाति (Kryadi 4), and मिनोति (मि of Svadi 4) for मि assumes the form मी by 6.4.16. Thus मित्सति, प्रमित्सति ॥ The मा denotes all the roots which assume the form मा, on the maxim गामादा ग्रहणेष्वविशेषः \The terms गा, मा or दा when they are employed in Grammar denote both the original roots गा, मा and दा and also the roots which are changed to गा, मा and दा\ ॥ They are मा and माङ माने,and मेङ् प्रणिदाने ॥ Thus मित्सते, अप मित्सते ॥ घु--दित्सति, धित्सति; रभ्-आरिप्सते, लभ्-आलिप्सते, शक्-शिक्षति, पत्-पित्सति, पद्-प्रपित्सते ॥ In the roots that end in a vowel, the स् of इस् is changed to त् by 7.4.49, and in the roots that end in a consonant, this स् is dropped, according to 8.2.29. The reduplication falls by 7.4.58.
Why do we say 'when the Desiderative follows'? Observe दास्यति ॥ The word सि is understood here from 7.4.49, so the rule will not apply when the Desiderative takes the augment इट्, as प्र पतिषति ॥ Here पत् optionally takes इट् under the vartika तनिपतिदरिद्राणामुपसंख्यानम् ॥
Vart:- The इस् comes after the root-vowel of राध् in the Desiderative, when the sense is that of to injure. As प्रति रित्सति ॥ Why do we say when the sense is that of 'to injure'? Observe आरि रात्सति ॥,