The affix ghañ comes after the roots 1. yu 'to join' 2. dru 'to run' 3. du 'to burn' when in composition with the preposition sam,
As संयावः, सन्द्रावः, सन्दावः । But प्रयवः where the preposition is not sam.,
समि यु-द्रु-दुवः
Adhyāya 3 · Pāda 3 · Rule 23