deriv SD cv (134) ashtadhyayi.com hei.de L 134 ETT STT a 6.1.134 ALPH OLDHOMEPAGE NEWHOMEPAGE

so 'ci lope cet pAda-pUraNam

सो ऽचि लोपे चेत्पादॱपूरणम् ONPANINI 61134

The /su of /sas may be erased before a vowel metri causa.

An example from the veda:

sauSadhIr anurudhyase सौषधीरनुरुध्यसे "into the plants thou forcest way" — Rg 8.43.9

Some say that this sUtra is vedic, others that it applies to the /laukika too. If it applies to the /laukika, then the saH सः + eSaH एषः in this /zloka are PC —

saiSa dAzarathI rAmaH | सैष दाशरथी रामः । "this one here is Raama son of Dasharatha"
saiSa rAjA yudhiSThiraH | सैष राजा युधिष्ठिरः । "this one the king Yudhishthira"
saiSa karNo mahAtyAgI | सैष कर्णो महात्यागी । "this one Karna the great giver"
saiSa bhImo mahAbalaH || सैष भीमो महाबलः ॥ "this one Bheema the very strong"

and otherwise this /zloka is sloppy, because these saiSa सैष should be corrected to sa::eSa स‌एष, screwing up the rythm.