The last vowel, with the consonant, if any, that follows it, is elided when the affixes 1. iṣṭha 2. iman and īyas follow.,
Thus पटिष्ठः, पटिमा, and पटीयान् from पटु, and लघिष्ठः, लघिमा and लघीयान् from लघु ॥
Vart:- The Pratipadika followed by the causative णि, undergoes all the changes, as it would have undergone, had the affix इष्ठ followed it. Those changes are (1) पुंवद्भावः the feminine noun becomes masculine: as, एमीमाचष्टे - एतयति, श्येतयति ॥ इष्ठ belongs to तसिलादि affixes and causes masculation by 6.3.35, (2) रभावः - the change of ऋ to र, as पृथुमाचष्टे - प्रथयति, म्रदयति, see 6.4.161. (3) टिलोपः - as, पटुमाचष्टे = पटयति, लघयति by this sutra, (4) यणादिपरम् i.e. the application of Rule 6.4.156, as, स्थूलमाचष्ट - स्थवयति ॥ According to the school of Bharadvaja, three more purposes are served : (5) विन् मतोलृक् - as स्रग्विणमाचष्टे = स्रजयति, वसुमन्तंमाचष्टे = वसयति, see 5.3.65. (6) कन्विधिः - the substitution of कन् for युवन् and अल्प. 5.3.64 - as युवानमाचष्टेः or अल्पमाचष्टे - कनयति ॥ (7) प्रादि substitution, as required by 6.4.157: as, प्रियमाचष्टे — प्रापयति ॥,