यीवर्णयोर्दीधीवेव्योः

Operational rule vidhi

The final of दीधी and वेवी falls before an affix beginning with य् , इ or ई.

Word by word (padaccheda)

Right context यीवर्णयोः saptamī · dvivacanaTarget दीधीवेव्योः ṣaṣṭhī · dvivacana

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).

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Full reading

यीवर्णयोः दीधीवेव्योः

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

Commentary

The final of दीधी and वेवी falls before an affix beginning with य् , इ or ई।
Thus आदीध्य and आवेष्य गतः, आदीध्यते, and आदेष्यते before य् ॥ आदीधितृ, आवेवितृ; आदीधीत and आवेवीत ॥ Why before य, इ or ई ? Observe आदीध्यनम् and आवेव्यनम् ॥ The long ई in यी is a sutra वैचित्र, for यिवर्णयोः would have been enough.

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