A long is substituted for the final vowel of the aṅga (stem) before the Adverbial affix cvi -- abhūtatadbhāve kṛbhvastiyoge sampadyakartari cviḥ [[5.4.50]].,
As शुची करोति, शुची स्यात्, शुची भवति, पटू करोति, पटू स्यात्, पटू भवति ॥ The च draws in the anuvritti of the phrase 'non-krit, and non-sarvadhatuka' from the last sutra, which though not of any direct use in this aphorism, is necessary for the sake of subsequent ones. See 7.4.32 for words ending in अ ॥,