2.4.66
बह्वचः इञः प्राच्यभरतेषु
Operational rule vidhi
And there is लुक् elision of the गोत्र affix इञ् -- गोत्राद्यून्यस्त्रियाम् (4.1.95) after a word containing many vowels (a poly-syllabic word) which denotes the गोत्र of the people called प्राच्य and भरत when the word takes the plural.
Word by word (padaccheda)
Left context बहु- pañcamī · ekavacanaTarget इञः ṣaṣṭhī · ekavacanaRight context प्राच्य- भरतेषु saptamī · bahuvacana
- Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.
Full reading
बहु-
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 इञ् -- गोत्राद्यून्यस्त्रियाम् 4.1.95 after a word containing many vowels (a poly-syllabic word) which denotes the गोत्र of the people called प्राच्य and भरत when the word takes the plural.
The plural of पन्नागारिः is पन्नागारः, there being elision of इङ् : so also नंथरेषणाः plural of नान्थरैषणिः; so the plural of यौधिष्ठिरिः is युधिष्ठिरा 'the descendents of Yudhishthira.' But यैकिः and पौष्पिः not being polysyllabic, their plural will be यैक्यः and पौष्प्यः.
Why do we say 'when denoting the Gotra of Prachyas and Bharatas'? Because when denoting the Gotra of any other people, these affixes will not be elided. Thus बालाकयः plural of बालाकिः, हस्तिदासयः plural of हस्तिदासिः.
Though the Bharatas are Prachyas, its specification here is to indicate that, wherever 'Prachyas' will be used, it will not include Bharatas as in 5.4.60. Here the Yuvan affix of Bharatas will not be elided. Thus आर्जुनिः father, आर्जुनायनः son.
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.