After the verbs kṛñ 'to do' and vṛṣ 'to rain', the affix kyap is optionally used.,
The root कृ would have taken the affix ण्यत्, by 124, and the verb वृष् would necessarily have taken क्यप् by 110; the present sutra therefore declares an optional rule. Thus: कृ + क्यप् = कृत्यम् 'to be done'; or कृ + ण्यत् = कार्यम्. So also वृष्यम् or वर्ष्यम् 'stimulating'.,