Reference for Yevamot 34:1
ראשונה לא משתבש מאי ראשונה ראשונה לנפילה ומאן דתני שניה לא משתבש מאי שניה שניה לנשואין מי לא עסקינן דיבם ואח"כ כנס אלא מאי שניה שניה בנשואין
FIRST commits no error', since 'first' may signify<span class="x" onmousemove="('comment',' Lit., 'what is first?' ');"><sup>1</sup></span> 'first to be subject [to the levirate marriage]'; and 'he who uses the expression SECOND also commits no error', since 'second' may signify 'second to marry',<span class="x" onmousemove="('comment',' The second brother who was already a married man when he contracted the levirate marriage with her. V. supra p 94. n. 4. ');"><sup>2</sup></span> Does not our Mishnah, however, include also<span class="x" onmousemove="('comment',' Lit., 'are we not engaged on'. ');"><sup>3</sup></span> the case of one who contracted the levirate marriage first and subsequently married his other wife?<span class="x" onmousemove="('comment',' In which case the widow was also the first to marry him. ');"><sup>4</sup></span>