After the words kim , yad and tad in determining of the one out of two, comes the affix ḍatarac (atara with the elision of the final im and ad).,
This affix comes in the svartha sense. The differentiation of a portion from the whole by means of its peculiar caste, action, attribute or name is called निर्द्धारण or specification. Thus कतरो भवतोः कठः 'amongst you two, who is Katha'. कतरो भवतोः कारकः 'amongst you two, who is the agent'. कतरो भवतोः पटुः 'amongst you two, who is clever'. कतरो भवतोः देवदत्तः 'which of the two amongst you is Devadatta'. Similarly यतरः 'of the two the one who', ततरः 'of the two--that one'. as यतरो भवतो देवदत्तः, ततर आगच्छतु 'of the two, let that one who is Devadatta, come'. The taddhita affixes being optional 4.1.82, this idea may be expressed by a sentence also. As, को भवतो देवदत्तः, स आगच्छतु 'who amongst you two is Devadatta, let him come'.,