Pāṇini sūtras

The penultimate vowels of a stem ending in in, han, pūṣan or aryaman are lengthened before the affix su of the Nominative Singular but not in Vocative Singular.

German Desgleichen im Nomin. Sg. (13)

1. sauसौ

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	suसु	sauसौ	suसु	sस् + plus auऔ

2. caच

   Part	Lexeme	Sandhi form	Meaning	Stem
   cच्	caच	caच	besides	caच

Anuvṛtti

1. na+upadhāyāḥन+उपधायाः 6·4·7

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   nन्	naन	naन	nakāraनकार	nन् + plus aअ
   uउ	upadhāउपधा	upadhāyāḥउपधायाः	penult	upadhउपध् + plus āyआय्

2. a+sambuddhauअ+सम्बुद्धौ 6·4·8

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	aअ	aअ	not	aअ
   sस्	sambuddhiसम्बुद्धि	sambuddhauसम्बुद्धौ	vocative	sambuddhसम्बुद्ध् + plus auऔ

3. in+han+pūṣa+aryamṇāmइन्+हन्+पूष+अर्यम्णाम् 6·4·12

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   iइ	inइन्	inइन्		inइन्
   hह्	hanहन्	hanहन्	hanहन्	hanहन्
   pप्	pūṣanपूषन्	pūṣaपूष	pūṣan [word]पूषन् [wओर्द्]	pūṣपूष् + plus aअ
   aअ	aryamanअर्यमन्	aryamṇāmअर्यम्णाम्	aryaman [word]	aryamअर्यम् + plus ṇण्