अचि र ऋतः

Thus तिस्रः, (in तिस्रस्तिष्ठन्ति, तिस्रः पश्य) चतस्रस्तिष्ठन्ति, चतस्रः पश्य ॥ प्रियतिस्र आनय, प्रियचतस्र आनय, प्रियतिस्रः त्वम्, प्रियचतस्रः त्वम् ॥ प्रियतिस्रि निधेहि, प्रियचतस्रि निधेहि ॥ This supersedes (VI. I. 102) (ordaining the single long substitution of the form of the first), (VI. I. 111) (substitution of उर् for ॠ), and 7.3.110 (the substitution of guna). The last rule 7.3.110, though subsequent in order, is however superseded by this rule. Why 'before the affixes beginning with a vowel?' Observe तिसृभिः, चतसृभिः ॥ The ॠतः of the sutra refers to the ॠ of तिसृ and चतसृ and not to a ॠ ending stem in general: and had it not been used in the sutra, the latter would have stood thus अचिरः \र् is substituted for the final of the words above-mentioned before an affix beginning with a vowel.\ So र् would have been substituted for the final of त्रि and चतुर् also.,