Responsa for Chullin 46:14

ספיקא הויא ונפיק ממה נפשך או דלמא בריה הוא ולא נפיק

Even so, that other person does not know whether to regard these [cakes of siur] as leavened and bring the unleavened himself, or to regard these as unleavened and bring the leavened himself!<span class="x" onmousemove="('comment',' The purpose of this man's promise is to release that other person from part of his obligation; but since the other cannot avail himself of these cakes, for he does not know what other cakes he must bring, this man's purpose has not been achieved and consequently his obligation has not been discharged.');">¹⁰</span>

Maharach Or Zarua Responsa