बह्वच्पूर्वपदाट्ठच्

Operational rule vidhi

The affix ठच् comes in the sense of 'this is whose act occurring in study' after a compound having polysyllabic word as a prior member.

Word by word (padaccheda)

Left context बहु- - पूर्वपदात् pañcamī · ekavacanaSubstitute / term ठच् prathamā · ekavacana

Left context Pañcamī (5th case): "after X", the operation applies to what follows (1.1.67 तस्मादित्युत्तरस्य). Also used for limits and sources.
Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.

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

बहु- -पूर्वपदात् ठच्

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

Commentary

The affix ठच् comes in the sense of 'this is whose act occurring in study' after a compound having polysyllabic word as a prior member.
This debars ठक् ॥ Thus:- द्वादशान्यानि कर्माण्यध्ययने वृत्तानि अस्य = द्वादशान्यिकः 'an examinee who commits twelve mistakes in his reading'. So त्रयोदशान्यिकः, चतुर्दशान्यिकः ॥ The word अन्यत् in these sutras means the 'error', especially in accent, i. e. he who makes an accent अनुदात्त which ought to be udatta, or vice versa.

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