क्यच्व्योश्च

Operational rule vidhi

The य् of a Patronymic affix, preceded by a consonant, is elided before the Denominative affix क्य and the adverbial affix च्वि.

Word by word (padaccheda)

Right context क्य- च्व्योः 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

क्य-च्व्योः च

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

Commentary

The य् of a Patronymic affix, preceded by a consonant, is elided before the Denominative affix क्य and the adverbial affix च्वि।
Thus वात्सीयति or वात्सीयते गार्गीयति, or गार्गीयते ॥ So also गार्गीभूतः, वात्सीभूतः ॥ But सांकाश्यायते (where य is not Patronymic) and so also सांकाश्यीभूतः; and not also in कारिकेयीयति, कारिकेयीभूतः, the य not being preceded by a consonant.

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