mum is the augment added immediately after the final vowel of arusa , dviṣat and of a stem ending in a vowel unless it is an indeclinable, when the word formed by a khit affix follows.,
Thus अरुन्तुदः, द्विषन्तपः, कालिंमन्या &c. See 3.2.35, 3.2.39, 3.2.83. The स् of अरुस् and the त् of द्विषत् are dropped by 8.2.23.
Why do we say 'of अरुस् &c'? Observe विद्वन्मन्या ॥ Why do we say 'not an Indeclinable'? Observe दोषामन्यमहः, दिवामन्यारात्रिः ॥ Why do we use the word अन्त in अजन्त, when merely saying अचः would have sufficed by the rule of tadanta-vidhi? This indicates that the shortening taught in the preceding sutra does not debar the मुम् augment, nor does मुम् debar the shortening. So that मुम् is added after the shortening has taken place.,