The affix ṅīp is not optionally used after a dvigu samāsa (Numeral Determinative Compound) where the taddhita affix is elided when the compound ends in the word puruṣa , referring to 'measure'.,
Thus द्विपुरुषा or द्विपुरुषी परिखा 'a mote two purusha wide' so also त्रिपुरुषी or त्रिपुरुषा &c. The present sutra ordains an option where 4.1.22 would have made the prohibition universal. Why do we say 'when referring to measure'? Observe द्विपुरुषा 'a female purchased in exchange for two males'; No option is allowed here. Where the Taddhita affix is not elided, the present rule does not apply. Therefore in Samahara Dvigu we have द्विपुरुषी or त्रिपुरुषी ॥,