Reference for Temurah 3:6

ותיסברא הכל ממירין לכתחילה

You say: ALL PERSONS CAN EXCHANGE, implying that it is [permissible to exchange in the first instance] and [then it says]: NOT THAT ONE IS PERMITTED TO EXCHANGE, implying, only after it has been done?<span class="x" onmousemove="('comment',' Is the exchange effective, but not that it is directly permissible.');">⁵</span>

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