Pāṇini sūtras

The augments rīk, ruk and rik come after the reduplicate of a root which has a ṛ in the penultimate, only when the yaṅ of the Intensive is elided.

1. ruk+rikauरुक्+रिकौ

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   rर्	rukरुक्	rukरुक्	rukरुक्	rukरुक्
   rर्	rikरिक्	rikauरिकौ	rikरिक्	rikरिक् + plus auऔ

2. caच

   Part	Lexeme	Sandhi form	Meaning	Stem
   cच्	caच	caच	besides	caच

3. lukiलुकि

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   lल्	lukलुक्	lukiलुकि	suffix elision	lukलुक् + plus iइ

Anuvṛtti

1. abhyāsasyaअभ्यासस्य 7·4·58

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	abhyāsaअभ्यास	abhyāsasyaअभ्यासस्य	reduplication	abhyāsअभ्यास् + plus asyaअस्य

2. ṛ+t+upadhasyaऋ+त्+उपधस्य 7·4·90

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   ṛऋ	ṛऋ	ṛऋ	ṛkāraऋकार	ṛऋ
   tत्	tत्	tत्	TT	tत्
   uउ	upadhāउपधा	upadhasyaउपधस्य	penult	upadhउपध् + plus asyaअस्य