Answer to a question "how does उपसर्ग become सुबन्तपद?"

प्र gains प्रातिपदिक-संज्ञा by 1.2.45
प्र gains निपात-संज्ञा by 1.4.58
प्र meaningfully connected to a धातु gains उपसर्ग-संज्ञा by 1.4.59
प्र meaningfully connected to a धातु also gains गति-संज्ञा by 1.4.60
प्र, being निपात, gains अव्यय-संज्ञा by 1.1.37
प्र, being प्रातिपदिक, is suffixed with सुँ by 4.1.2
प्र being अव्यय, सुँ is elided by 2.4.82
प्र is सुबन्तं पदम् by 1.4.13

प्र, being उपसर्ग/गति, is placed before धातु by 1.4.80

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