ङसिङसोश्च

Operational rule vidhi

If an एकार or ओकार is followed by the अकार of ङसिँ or ङस् प्रत्यय, then both of them combined to form a पूर्वरूप एकादेश.

Word by word (padaccheda)

Right context ङसि- ङसोः saptamī · dvivacanaIndeclinable च avyaya

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").
Indeclinable An avyaya such as च "and", वा "optionally", न "not".

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

ङसि-ङसोः च

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

Commentary

In the room of ए or ओ (in the body of a word), + अ of the case-affix अस् of the Ablative and Genitive Singular, the single substitute is the form of the precedent.
Thus अग्ने + अस् = अग्नेः, वायोः ॥ The इ and उ of अग्नि and वायु are gunated by 7.3.111. This sutra applies when the ए or ओ are in the middle of a word and not padanta, as in the last. Thus अग्नेरागच्छति, वायोरागच्छति, अग्नेः स्वम्, वायोः स्वम् ॥

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