The 5th case-affix (Ablative) is used after whatsoever is governed by a karmapravacanīyāḥ [[1.4.83]] in the sense of 'substitute' or 'exchange' -- pratiḥ pratinidhipratidānayoḥ [[1.4.92]].,
Ex. अभिमन्युरर्जुनतः प्रति 'Abhimanyu is the representative of Arjuna.' माषानस्मैतिलेभ्यः प्रतियच्छति 'he exchanges mashas for this sesamum.' See 1.4.92 for an explanation of प्रतिनिधि and प्रतिदान.,