The affix vun comes in the sense of 'who studies or who knows' after the words krama etc.,
This debars अण् ॥ Thus क्रमकः 7.1.1 &c. The words 1 क्रम, 2 पद, 3 शिक्षा, 4 मीमांसा, 5 सामन् belong to this class.,
क्रमादिभ्यो वुन्
Adhyāya 4 · Pāda 2 · Rule 61