deriv SD cv (213) ashtadhyayi.com hei.de L 213 ETT STT a 7.2.102 ALPH OLDHOMEPAGE NEWHOMEPAGE

tyad-AdInAm aH

त्यदादीनामः ONPANINI 72102

Replace the /tyadAdi with a अ (before /vibhakti).

The /tyadAdi (or /tyad--class) are these eight pronouns —

/tyad- /tad- /yad- /etad-
/idam- /adas- /eka- /dvi-

Because of alontyasya and atoguNe, the "replace with a अ" operation turns these into —

tya- त्यॱ ta- तॱ ya- यॱ eta- एतॱ
ida- इदॱ ada- अदॱ eka- एकॱ dva- द्वॱ

As for instance in —

/tad- m + /TA
→ **ta- तॱ + /TA
→ **tena तेन, like **azvena अश्वेन

where the /tad- lost its d द् by this rule and atoguNe.

Why "before vibhakti"?

The replacement will not happen when there is no /vibhakti, either because of svamornapuMs... —

/tad- n + /su OR /am
→ !**tad' तद्ऽ n "it"

or because of supodhAtupr... —

/tad- + **puruSa- पुरुषॱ
→ !**tatpuruSa- तत्पुरुषॱ m "that man" (this is a /tatpuruSa-class compound)