ऋत्यकः

Operational rule vidhi

According to शाकल्य, In the context of संहिता a पदान्त-अक्-letter, when followed by a ह्रस्व ऋ/ऌ-letter undergoes ह्रस्वादेशः and then no other sandhi happens.

Word by word (padaccheda)

Right context ऋति saptamī · ekavacanaTarget ṣaṣṭhī · ekavacana

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").
Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).

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

ऋति

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

Commentary

According to the opinion of शाकल्य , the simple vowel followed by ऋ retains its original form, and if the vowel is long, it is shortened.
Thus खट्वा ऋश्यः, कुमारि ऋश्यः, होतृ ऋश्यः ॥ Why do we say when followed by ऋ? Observe, खट्वेन्द्रः ॥ Why do we say "the simple vowels (अकः)"? Observe वृक्षावृश्यः (वृक्षा + ऋश्य) ॥ This rule applies even when the vowels are homogenous (which were excepted by the last rule), and it is not confined to इक् vowels as the last, but applies to अ and आ also.

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