The seṭ ktvā is optionally kit , according to the opinion of ṛṣi kāśyapa after the verbs tṛṣ 'to be thirsty', mṛṣ 'to sprinkle' and kṛś 'to become lean'.,
As तृषित्वा or तर्षित्वा 'having thirsted,' मृषित्वा or मर्षित्वा 'having sprinkled,' कृशित्वा or कर्शित्वा 'having become lean.' By sutra 1.2.18, the set ktva is never kit. This sutra adds another exception to that general rule.
The special mention of Kasyapa is for the sake of showing respect. The वा is already understood in this sutra by Anuvritti from sutra 1.2.23.,