In the room of anusvārā, when yay follows, a letter homogenous with the latter is substituted.,
Thus शङ्किता, शङ्कितुम्, शङ्कितव्यम्, उञ्छिता, कुण्डिता, नन्दिता, कम्पिता &c. These are from roots शकि शङ्कायाम्, उञ्छि उञ्छे, कुदिदाहे, टुनदि समृद्धौ, कपि चलने ॥ Here नुम् is added because they are उदित्, and this न् becomes anusvara by 8.3.24, and this anusvara is changed to ङ् when followed by a guttural क् &c, to ञ् when followed by a palatal च &c, and so on to ण्, न् and म् ॥
Why do we say 'when यय् follows'? Observe आक्रंस्यते, आचिक्रंस्यते ॥
In कुर्वन्ति, वृषन्ति, the न is not changed into ण, though required by 8.4.2. Because the णत्व is asiddha, and therefore by the prior rule 8.3.24, the न is first changed into anusvara 8.2.1. That anusvara is again changed into न by the present rule, न being homogeneous with त ॥ This change again being असिद्ध as if it had never taken place 8.2.1, the ण is never substituted for न ॥,