2.4.64
यञञोश्च
Operational rule vidhi
And there is लुक् elision of the गोत्र affix यञ् -- गर्गादिभ्यो यञ् (4.1.105) and अञ् -- अनृष्यानन्तर्ये बिदादिभ्योऽञ् (4.1.104), when the word of itself and not as part of a compound epithet dependent on another, takes the plural, but not in the feminine.
Word by word (padaccheda)
Target यञ्- अञोः ṣaṣṭhī · dvivacanaIndeclinable च avyaya
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- Indeclinable An avyaya such as च "and", वा "optionally", न "not".
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Full reading
यञ्-
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
And there is लुक् elision of the गोत्र affix यञ् -- गर्गादिभ्यो यञ् 4.1.105 and अञ् -- अनृष्यानन्तर्ये बिदादिभ्योऽञ् 4.1.104, when the word of itself and not as part of a compound epithet dependent on another, takes the plural, but not in the feminine.
गर्ग + यञ् = गार्ग्यः; plural गर्गाः 'the male descendents of Garga'. So also वत्साः 'the male descendents of Vatsa'; the singular being, वात्स्यः Similarly, विद + अञ् = वैदः 4.1.104; plural विदाः and not वैदाः; similarly और्व singularly; और्वाः plural.
But these affixes are not elided when the word forms part of a compound. Thus, प्रियगार्ग्याः those to whom Gargya is beloved;' प्रियवैदाः 'those to whom Baida is beloved.'
These affixes will not be elided in the feminine. Thus, गार्ग्यः, वैद्य, feminine plurals.
Of course these affixes must be Gotra or patronymic affixes, otherwise there will be no elision. Thus द्वीप + यञ् = द्वैप्यः 'living on the island,' plural द्वैप्याः; here the affix यञ् is not elided as it does not denote a Gotra. So उत्स + यञ् = औत्सः 'the pupil of Utsa,' plural औत्साः.
Vart:- In forming Tat-purusha compound of the singular and dual genitive, the affix यञ् and अञ् are optionally elided. Thus गार्ग्यस्य कुलं = गार्ग्यकुलं or गार्गकुलं, गार्ग्ययीः कुलं = गार्ग्यकुलं or गर्गकुलं.
Similarly वैदस्य or वैदयोः कुलं = वैदकुलं or विदकुलं.
Why do we say 'the affixes यञ् or अञ्'? Because other affixes will not be elided in forming तत्पुरुष compound; such as आङ्गकुलं ।
Why do we say 'singular or dual'? Because in the plural तत्पुरुष compounds, these affixes must necessarily be elided and not optionally; thus गर्गाणां कुलं = गर्गकुलं.
Why do we say 'in forming तत्पुरुष compound'? Because in forming other compounds, these affixes will not be elided. Thus, उपगार्ग्य which is an अव्ययीभाव compound, meaning गार्गस्य समीपं. Of course, it is only in the Genitive तत्पुरुष that this rule is applicable; it will not therefore apply in कर्मधारय तत्पुरुष &c., as परमगार्ग्यः ।
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.