The substitute dhamuñ comes optionally in the place of dhā after the words 1. dvi and 2. tri,
Here also it comes in both the विधार्थ and अधिकरण विचाल senses. By च, the word 'optionally' is drawn into the sutra. Thus द्विधा or द्वैधम्, त्रिधा, or त्रैधम् ॥
Vart:- The affix ड (da, with the elision of the final vowel) comes without changing the sense, after words ending in dhamun. As द्वैध, त्रैध, in पथि द्वैधानि संश्रयन्ते, मति त्रैधानि संश्रयन्ते ॥,