अणुदित् सवर्णस्य चाप्रत्ययः

The letters of the प्रत्याहार अण् i.e. the vowels and semi-vowels and a term having उ for its indicatory letter, refer to their own form as well as to their homogeneous letters, except when they are used as प्रत्यय-s or affixes.
The pratyahara अण् in thus sutra includes all the vowels and liquids. This is the only instance where अण् pratyahara refers to the second ण् of लण्. The letters included in अण्, and the letters having an indicatory उ, refer to, and include their homogeneous letters also. Thus कु refers to all the five gutturals क, ख, ग, घ, ङ, similarly चु, टु, तु, and पु, as in sutra (1.3. 8). Similarly अ includes short, long and protracted अ. The words 'its own form' are understood in this sutra, being drawn from the previous sutra. Thus sutra आद्गुणः 6.1.87, 'when a vowel comes after अ, guna is the single substitute for both.' Here though the rule mentions only short अ, we take the long आ also. Thus not only नर + ईशः = नरेशः; but महा + ईशः = महेशः । So also in sutra अस्य च्वौ 7.4.32, 'there is long ई in the room of अ when the affix 'chvi' 5.4.50 follows.' Here long आ is also included; thus कृष्ण + करोति = कृष्णीकरोति, and खट्वा + करोति = खट्वीकरोति. So also in sutra यस्येति च 6.4.148. 'When long ई follows, there is elision of the इ or अ of the base,' the rule applies to the bases ending in long ई and आ also.

This rule of course does not apply to affixes. Thus sutra 3.2.168, says, 'after words ending in the affix san, and the words asansa and bhiksha, there is उ.' Here उ is an affix and therefore does not include long ऊ. Thus भिक्षुः 'a beggar.' So also in 4.3.9, the short अ only is to be taken and not the long one.