न-उपधात् थ-फ-अन्ताद् वा

The set ktva may or may not be kit after the verbs ending in थ् or फ् preceded by a nasal. The result of being kit will be that nasal will be dropped. In other words the dropping of the nasal is optional in such verbs. Thus from ग्रंथ् we have ग्रथित्वा or ग्रन्थित्वा 'having twisted,' गुफित्वा or गुंफित्वा 'having tied round', श्रथित्वा or श्रन्थित्वा.

The word \Nishtha\ does not govern this sutra, and comes to an end with the last sutra.

This rule does not apply to verbs that have not a penultimate न् though they may end in थ् or फ्. As रेफित्वा 'having reviled', गोफित्वा 'having tied.' Here by rule 18, the त्वा tva being non-kit, the vowels of the root रिफ् and गुफ् have been gunated.

A verb may have a penultimate न्, but if it has not final थ or फ, the rule does not apply. As स्रंस् + इत्वा = स्रंसित्वा 'having dropped', ध्वंसित्वा 'having killed.' Had it been kit, the nasal would have been dropped.,