व्रजयजोर्भावे क्यप्

Operational rule vidhi

The affix क्यप् comes after a roots 1. व्रज 'to go' 2. यज् 'to worship' acutely accented (उदात्त) in forming a word in the feminine denoting action.

Word by word (padaccheda)

Target व्रज- यजोः ṣaṣṭhī · dvivacanaRight context भावे saptamī · ekavacanaSubstitute / term य prathamā · ekavacana

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").
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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Pink letters are it-markers (anubandhas), tags dropped by 1.3.9. Hover or tap one for the rule that marks it, or try the it-letter finder.

Full reading

व्रज-यजोः भावे क्यप्

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

As a rewrite rule (sketch from case endings)

व्रज- यजोः → क्यप् / भावे

Replace vraja-yajoḥ with kyap when bhāve follows. Inherited words (anuvṛtti) may add further conditions.

Commentary

The affix क्यप् comes after a roots 1. व्रज 'to go' 2. यज् 'to worship' acutely accented (उदात्त) in forming a word in the feminine denoting action.
This supersedes क्तिन्. Thus व्रज्या 'wandering about'; इज्या 6.1.15 'worshipping'. The प् of क्यप् is indicatory, and though it serves no purpose in this sutra, it is, however, necessary in the next, for it is by force of क्यप् having प् that we add a त by 5.1.7, in the words formed in the next aphorism.

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.