किमिदंभ्यां वो घः

Operational rule vidhi

After the words किम् and इदम् , घ (इय्) is substituted for the व् of वतुप्.

Word by word (padaccheda)

Left context किमिदम्भ्याम् pañcamī · dvivacanaTarget वः 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.

Dotted words are technical terms. Hover or tap one to see its card.

Full reading

किमिदम्भ्याम् वः

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)

वः → / किमिदम्भ्याम्

Replace vaḥ with ghaḥ when it comes after kimidambhyām. Inherited words (anuvṛtti) may add further conditions.

Commentary

After the words किम् and इदम् , घ (इय्) is substituted for the व् of वतुप्।
Thus किम् + वतुप् की + वतुप् 6.3.90 = क् + घतुप् 6.4.148 = कियत् nom. कियान्. Similarly इयत् nom. इयान् ॥

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