कुमारशीर्षयोर्णिनिः

Operational rule vidhi

The affix णिनि comes after the verb हन् 'to kill' when the word in composition with it is कुमार 'a child' or शीर्ष 'head'.

Word by word (padaccheda)

Right context कुमार- शीर्षयोः saptamī · dvivacanaSubstitute / term इ ः prathamā · ekavacana

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.

Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.

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Full reading

कुमार-शीर्षयोः णिनिः

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

Commentary

The affix णिनि comes after the verb हन् 'to kill' when the word in composition with it is कुमार 'a child' or शीर्ष 'head'.
The affix णिनि comes after the verb हन् 'to kill' when the word in composition with it is कुमार 'a child', or शीर्ष 'head'.

Thus कुमार + हन् + णिनि = कुमार + घात + इन् 7.3.54 and 7.3.32 = कुमारघातिन् nom. sing. कुमारघाती 'child-killer'. So also शीर्षघातिन् nom. sing. शीर्षघाती 'head-killer'.

The word शीर्ष is an irregular form of the word शिरस् ।

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