6.3.102
रथवदयोश्च
Operational rule vidhi
कत् is substituted for कु before रथ and वद.
Word by word (padaccheda)
Right context रथ- वदयोः 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".
Full reading
रथ-
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
कत् is substituted for कु before रथ and वद।
Thus कद्रथः, कद्वदः ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.