deriv SD cv (338) ashtadhyayi.com hei.de L 338 ETT STT a 7.2.106 ALPH OLDHOMEPAGE NEWHOMEPAGE

tados sas sAv an-antyayoH

तदोः सः सावनन्त्ययोः ONPANINI 72106

Replace nonfinal t त् d द् (of the /tyadAdi) with s स् before /su.

So we have

masculine syas स्यस् **sas सस् **eSas एषस्
feminine syA स्या **sA सा eSA एषा.

but

neuter tyad त्यद् **tat तत् **etat एतत्

Those are derived like this —

/tad m + /su
→ ta त + s स् by <<<< tyadAdInAmaH ff
→ **sas सस् by this rule

/tad- f
→ ta- तॱ f by <<<< tyadAdInAmaH
→ ta- तॱ + /Ap by ajAdyataSTAp
→ tA- ताॱ + by akassa अकःस
→ **tA- ताॱ f "she, her, it, they"

/tad- f + /jas OR /zas
→ **tA- ताॱ f + /jas OR /zas
→ **tA- ताॱ f + s स् by dIrghAjjasica or by prathamayoHp...
→ ta- तॱ f by <<<< tyadAdInAmaH
→ ta- तॱ + /Ap by ajAdyataSTAp
→ !**tAs तास् f "they"

/tad- f + /su
→ **tA- ताॱ f + /su
→ sA- साॱ + /su by this rule
→ sA सा by halGyAbbhyodIrgh...
→ !**sA सा "she"

/etad- m + /su
→ esas एसस्, same steps as **sas सस्
→ !**eSas एषस्, with /Satvam

Why "before /su"?

When the /su is deleted by svamornapuMs... or supodhAtupr... this rule doesn't apply.

/tad- n + /su
→ tad तद् by svamornapuMs...
→ !**tat तत् "it", normalizing

/tad- m + /su + puruSas पुरुषस् → tatpuruSas तत्पुरुषस्

And of course it won't apply before non-/su endings —

/tad- m + /am → ta त + /am by <<<< tyadAdInAmaH → !**tam तम् by amipUrvaH

/tad- f + /am → **tA- ताॱ f + /am → !**tAm ताम् by amipUrvaH