The augment num is optionally added to labh 'to get' not preceded by a Preposition before the ciṇ Aorist and the Absolutive ṇamul,
Thus अलाभि or अलम्भि, लाभंलाभम् or लम्भंलम्भम् ॥ This is a Vyavasthita-vibhasha, the option is allowed where there is no Preposition along with the root; and no option is allowed but नुम् must be added, when a Preposition precedes: as प्रालम्भि, प्रलम्भम् ॥,