तोर्लि

Operational rule vidhi

A letter of तवर्ग is converted to a परसवर्ण when followed by a लकार.

Word by word (padaccheda)

Target तोः ṣaṣṭhī · ekavacanaRight context लि saptamī · ekavacana

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

Full reading

तोः लि

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

Commentary

In the room of तु (a dental) when the letter ल follows, one homogenous with the latter is substituted.
Thus अग्निचित् + लुनाति = अग्निचिल्लुनाति, सोमसुल्लुनाति; भवान् + लुनाति = भवाँल्लुनाति, महाँल्लुनाति ॥ Here त has been changed to pure ल, while the dento-nasal न् is changed to a nasal लँ ॥

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