After the verb ūrṇa 'to cover', the affix beginning with the augment iṭ is regarded optionally like ṅit,
Thus before the इडादि termination इता of the future, we may have either प्रोर्णुविता or प्रोर्णविता \he will cover.\
The equation of the form is :- प्र + ऊर्णु + इ + ता = प्र + ऊर्णुव् + इता 6.4.77 = प्रोर्णुविता. When the affix is not regarded as ङित्, it produces guna, and we have the second form प्रोर्णविता ॥
Of course there is no option allowed before those affixes which do not take the augment इट्, and before those terminations, consequently, we have only one form : as प्रोर्णु + ल्युट् = प्रोर्णो + अनम् = प्रोर्णवनम्, 'covering,' प्रोर्णवनीयम् 'which ought to be covered.',