a. The derived feminine stem in inī is inflected, of course, like any other feminine in derivative ī (364).
441. a. There are no irregularities in the inflection of in-stems, in either the earlier language or the later — except the usual Vedic dual ending in ā instead of āu.
b. Stems in in exchange with stems in i throughout the whole history of the language, those of the one class being developed out of those of the other often through transitional forms. In a much smaller number of cases, stems in in are expanded to stems in ina: e.g. çākiná (RV.), çuṣmiṇa (B.), barhiṇa, bhajina.
442. These stems fall into two sub-divisions: 1. those made by the suffix अन्त् ant (or अत् at), being, with a very few exceptions, active participles, present and future; 2. those made by the possessive suffixes मन्त् mant and वन्त् vant (or मत् mat and वत् vat). They are masculine and neuter only; the corresponding feminine is made by adding ई ī.
443. The stem has in general a double form, a stronger and a weaker, ending respectively in अन्त् ant and अत् at. The former is taken in the strong cases of the masculine, with, as usual, the nom.-acc.-voc. pl. neuter; the latter is taken by all the remaining cases.
a. But, in accordance with the rule for the formation of the feminine stem (below, 449), the future participles, and the present participles of verbs of the tud-class or accented á-class (752), and of verbs of the ad-class or root-class ending in ā, are by the grammarians allowed to make the nom.-acc.-voc. du. neut. from either the stronger or the weaker stem; and the present participles from all other present-stems ending in a are required to make the same from the strong stem.
444. Those verbs, however, which in the 3d pl. pres. active lose न् n of the usual ending न्ति nti (550 b), lose it also in the present participle, and have no distinction of strong and weak stem.