The affixes ṇamul and kamul are added to roots in the chandas (Vedas) to form Infinitives, when they are governed by the verb śak 'to be able'.,
Of the affix णमुल् the real affix is अम्; the letter ण् causes vriddhi 7.2.115; and ल regulates the accent (VI. I. 193). So also of कमुल्, the letter क् prevents guna and vriddhi substitution (I. I. 5).
Thus अग्निं वै देवा विभाजं नाशक्नुवन् 'the Gods were not able to divide Agni'. विभज् +णमुल् = विभाजं = विभक्तुम् । So also अपलुपं नाशक्नुवन्, instead of अपलोप्तुम् ।,