द्विषत्परयोस्तापेः

Operational rule vidhi

The affix खच् comes after the verb ताप् 'to heat' when द्विषत् or पर is the word in composition with it as an object.

Word by word (padaccheda)

Right context द्विषत्- परयोः saptamī · dvivacanaLeft context तापेः pañcamī · 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").
Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.

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

द्विषत्-परयोः तापेः

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

Commentary

The affix खच् comes after the verb ताप् 'to heat' when द्विषत् or पर is the word in composition with it as an object.
The verb तप् belongs both to Bhu and Chur classes. Both are meant in the sutra. In the case of Bhvadi, the verb तापि is the causative ending in णि of तप्; while in Churadi, all verbs take णि.

Thus द्विषन्तं तापयति = द्विषन्तपः 6.4.94 'one who destroys his enemies', so also परन्तपः 'one who subdues his enemies, a hero'.

This affix however, will not apply when the above upapadas are in the feminine gender. In this case the general affix अण् will be employed; as द्विषतीं तापयति = दिषतीतापः ।

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