The augment kuk optionally comes after a stem ending with the word putra when the Patronymic affix phin follows.,
The anuvritti of the words \according to the opinion of Northern Grammarians when the word has a Vriddhi in the first syllable\ must be read into this sutra. Of course, a word ending in पुत्र cannot be a Gotra-word, for a Gotra word means a grandson or a still lower descendant. Hence a word ending in पुत्र having Vriddhi in the first syllable will take the affix फिञ् by (IV. I. 157); the present aphorism only rules that it takes the augment कुक् optionally.
Thus we have three forms :- गार्गीपुत्रकायणिः or गार्गीपुत्रायणिः or गार्गीपुत्रिः ॥ So also वात्सीपुत्रकायणिः, वात्सीपुत्रायणिः and वात्सीपुत्रिः ॥,