Reference for Rosh Hashanah 4:6

מת באדר ועמד אחר תחתיו בניסן מונין ראשונה לראשון ושניה לשני פשיטא לא צריכא דאימנו עליה מאדר ומלך בן מלך הוא מהו דתימא נימנו לי' תרתין שנין קמ"ל

If the first died in Adar and he was succeeded by another in Nisan, the earlier year is dated by the first and the later by the second'. This surely is obvious? - It had to be stated i view of the case where his election was determined upon from Adar and he is succeeding his father.<span class="x" onmousemove="('comment',' This point is mentioned here because we have already been told above that his mere election does not affect the dating.');">⁶</span> In that case you might think that we should reckon two years to him.

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