There is optionally luk elision of the yuvan affixes phak and phiñ when a prāgdīvyatīya affix beginning with a vowel is to be added.,
By the last sutra, all Yuvan affixes were told to be elided. The present sutra declares an option in the case of the Yuvan affixes फक् and फिञ्. Thus the patronymic of गर्ग is गार्ग्य 4.1.105; the Yuvan of गार्ग्य is formed by फक् 4.1.101 गार्ग्यायणः ॥ The word denoting the pupils of Gargyana will be गार्गीय or गार्ग्यायणीयाः; वात्सीयाः or वात्सयायनीयाः ॥ Similarly of the affix फिञ् 4.1.156. Thus from यस्क, the Patronymic is यास्क 4.1.112. The Yuvan of the latter is यास्कायनि 4.1.146. The pupils of Yaskayani will be called यास्कीया or यास्कायनीयाः ॥,