deriv SD cv (133) ashtadhyayi.com hei.de L 133 ETT STT a 6.1.132 ALPH OLDHOMEPAGE NEWHOMEPAGE

etat;tados su-lopo 'kor a-naJ-samAse hali

एतत्तदोः सुॱलोपो ऽकोरॱनञ्समासे हलि ONPANINI 61132

Before consonants, (in /saMhitA,) delete the /su of /tad- and /etad-, unless they have /akac or have /naJ ibc.

When /tad- and /etad- have /su, they become **sas सस् and **eSas एषस्. Then, this sUtra deletes their final s स् when any consonant follows in /saMhitA —

/sas + dravati द्रवति
→ !**sadravati सद्रवति "he's running" by this rule

/sas + **chinatti छिनत्ति
→ sa स + **chinatti छिनत्ति by this rule
→ **sacchinatti सच्छिनत्ति "he cuts", by checa

If any vowel follows, the usual sandhi of final as will hide the s स् —

/sas + Agacchati आगच्छति → !**sa::Agacchati स‌आगच्छति "he's coming" like **arjuna::uvAca अर्जुन‌उवाच

/sas + **abravIt अब्रवीत् → !**sobravIt सोब्रवीत् "he said"

so, the s only survives before a pause, as H ः of course —

dravati saH द्रवति सः "he's running".