6.4.153
बिल्वकादिभ्यश्छस्य लुक्
Operational rule vidhi
The affix छ of the भ अङ्ग (stems) बिल्वक etc. is elided before a तद्धित affix.
Word by word (padaccheda)
Left context बिल्वकादिभ्यः pañcamī · bahuvacanaTarget छस्य ṣaṣṭhī · ekavacanaSubstitute / term prathamā · ekavacana
- 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).
- Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
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Full reading
बिल्वकादिभ्यः छस्य
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
छस्य → / बिल्वकादिभ्यः
Replace chasya with luk when it comes after bilvakādibhyaḥ. Inherited words (anuvṛtti) may add further conditions.
Commentary
The affix छ of the भ अङ्ग (stems) बिल्वक etc. is elided before a तद्धित affix.
The बिल्व &c are a subdivision of Nadadi class 4.2.91, and the augment क is added to them by 4.2.91. After these words, with the augment क, the affix छ is elided. Thus बिल्वा यस्यां सन्ति = बिल्वकीयाः; तस्यां भवाः 4.3.53 = बैल्वकाः ॥ Similarly वेणुकीयाः - वैणुकाः, वैत्रकीयाः, वैत्रकाः, वेतसकीयाः, वैतसकाः, तृणकीयाः, तार्णकाः इक्षुकीयाः, ऐक्षुकाः, काष्ठकीयाः, काष्ठकाः, कपोतकीयाः, कापोतकाः ॥ There is shortening of the final of क्रुंचा by the Vartika क्रुञ्चा ह्रस्वत्वं च ॥ क्रुञ्चकीयाः, क्रौञ्चकाः ॥ छग्रहणं किम्, छमात्रस्य लुग्यथा स्यात् कुको निवृत्तिर्मा भूदिति, ॥ अन्यथा हि संनियोगशिष्टानामन्यतापाये उभयोरप्यभाव इति कुगपि निवर्त्तेत ॥ लुग्ग्रहणं सर्वलोपो यथा स्याद् यकारमात्रस्य मा भूत् ॥
The affix छ is specifically mentioned in order to show that the affix only should be elided and not the augment क ॥ Otherwise क् would also have been elided on the strength of the maxim :- संनियोगशिष्टानामन्यतरापाये (or अभावे) उभयोरप्यभावः (or अपायः), "When of the two things which are taught together, one disappears, then the other disappears likewise". The लुक् indicates the elision of the whole affix ईय, and not merely of य ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.