Reference for Yevamot 218:11
אמר ליה היינו טעמא דר"ג משום דקסבר המקדש אחות יבמה נפטרה יבמה והלכה לה אי בעל אין אי לא בעל לא
Is it because he holds the opinion that the betrothal of a minor remains in a suspended condition<span class="x" onmousemove="('comment',' During her minority. ');"><sup>29</sup></span> and as she grows up it grows with her<span class="x" onmousemove="('comment',' I.e., becomes retrospectively effective as soon as she attains her majority. ');"><sup>30</sup></span> even though no cohabitation has taken place;<span class="x" onmousemove="('comment',' After her majority. As the validity of the original betrothal is thus made retrospective, the provisional levirate bond between the levir and the elder sister may be regarded as never having existed. ');"><sup>31</sup></span>