7.4.51
रि च
Operational rule vidhi
The last letter (सकार) of the तास्-प्रत्यय is removed when followed by a रेफ.
Word by word (padaccheda)
Right context रि saptamī · ekavacanaIndeclinable 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".
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Full reading
रि च
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
Commentary
The final स् of तास् (the character of the second future) and अस् 'to be' is elided before an affix beginning with र्।
As कर्तारौ, कर्त्तारः, अध्येतारौ, अध्येतारः ॥ The स् of अस् 'to be' is elided in the Perfect, because it is there that a र् beginning affix can follow it. Thus व्यतिरे (See 6.4.111. According to the reading of Padamanjari, there can be no example of अस् ॥ अस्तेरुदाहरणं न प्रदर्शितं, रेफादेरसम्भवात् ॥
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.