deriv SD cv (227) ashtadhyayi.com hei.de L 227 ETT STT a 6.4.11 ALPH OLDHOMEPAGE NEWHOMEPAGE

ap;tRn;tRc; svasR;naptR;neSTR;tvaSTR; kSattR;hotR;potR;prazAstRRNAm

अप्तृन्तृच्स्वसृॱनप्तृॱनेष्टृॱत्वष्टृॱ क्षत्तृॱहोतृॱपोतृॱप्रशास्तॄणाम् ONPANINI 64011

(Before strong endings except the /sambuddhi, lengthen the nexttolast — )
of /ap-,
/tRn /tRc -enders
and svasR स्वसृ naptR नप्तृ neSTR नेष्टृ tvaSTR त्वष्टृ kSattR क्षत्तृ hotR होतृ potR पोतृ prazastR प्रशस्तृ.

The nounbase /ap- f means "waters" and hearsay is that it is used only in the plural, so its only strong ending is /jas —

/ap- + /jas → !**Apas आपस् " s waters" by this rule

/ap- + /zas → !**apas अपस् " o waters" JBJ

All R ऋ bases are subject to RtoGisarv..., that turns R ऋ into ar अर् before a strong, like this —

pitR- पितृॱ + /am
→ pitar- पितर् + /am by RtoGisarv...
→ **pitaram पितरम् " o father"

!**mAtaram मातरम् " o mother"

So the nexttolast of the stem is a अ. This sUtra lengthens that a अ in some cases —

**svasR- स्वसृॱ f + /am
→ svasar- स्वसर् + /am by RtoGisarv... and uraNraparaH
→ **svasAram स्वसारम् " o sister" by this rule

**kSattR- क्षत्तृॱ m + /au → !**kSattArau क्षत्तारौ "two charioteers"

**kartR- कर्तृॱ m + /am → **kartAram कर्तारम् " o maker, doer"

Why didn't you show any examples with /su?

There aren't any. Before /su that is not /sambuddhi, Rduzanasp... overrides aptRn अप्तृन् —

**pitR- पितृॱ + /su → **pitA पिता

**svasR- स्वसृॱ + /su → **svasA स्वसा

**kartR- कर्तृॱ + /su → **kartA कर्ता

Now that you mention the /sambuddhi...

Okay, gotcha —

he svasar हे स्वसर् "hi sis!"