Pāṇini sūtras

The affix ach comes after the word râtri, when preceded by ahan, or sarva, or a word denoting a portion of night, or saṅkhyâta or punya, when the compound is a Tatpurusha, as well as when a Numeral or an Indeclinable precedes the word râtri.

1. ahar+sarva+eka+deśa+saṃkhyāta+puṇyātअहर्+सर्व+एक+देश+संख्यात+पुण्यात्

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	aharअहर्	aharअहर्	ahar [word]	aharअहर्
   sस्	sarvaसर्व	sarvaसर्व	sarva [word]	sarvaसर्व
   eए	ekaएक	ekaएक	eka [word]	ekaएक
   dद्	deśaदेश	deśaदेश	deśa [word]देश [wओर्द्]	deśदेश् + plus aअ
   sस्	saṃkhyāसंख्या	saṃkhyātaसंख्यात	enumerate	saṃkhyātसंख्यात् + plus aअ
   pप्	puṇyaपुण्य	puṇyātपुण्यात्	puṇya [word]पुण्य [wओर्द्]	puṇyपुण्य् + plus ātआत्

2. caच

   Part	Lexeme	Sandhi form	Meaning	Stem
   cच्	caच	caच	and	caच

3. rātreḥरात्रेः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   rर्	rātriरात्रि	rātreḥरात्रेः	rātri [word]रात्रि [wओर्द्]	rātrरात्र् + plus eḥएः

Anuvṛtti

1. samāsa+antāḥसमास+अन्ताः 5·4·68

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	samāsaसमास	samāsaसमास	Sanskrit compound	samāsसमास् + plus aअ
   aअ	antaअन्त	antāḥअन्ताः	end	antअन्त् + plus āMआM

2. acअच् 5·4·75

   Part	Lexeme	Sandhi form	Meaning	Stem
   aअ	acअच्	acअच्	acअच्	acअच्

3. saṅkhyā+avyaya+ādeḥसङ्ख्या+अव्यय+आदेः 5·4·86

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   sस्	saṃkhyāसंख्या	saṅkhyāसङ्ख्या	numeral	saṃkhyसंख्य् + plus āआ
   aअ	avyayaअव्यय	avyayaअव्यय	particle	avyayअव्यय् + plus aअ
   āआ	ādiआदि	ādeḥआदेः	beginning	ādआद् + plus eḥएः