Responsa for Yevamot 61:10

וממאי דמתניתין דהכא בכת אחת דומיא דקדושין מה קדושין בכת אחת אף גרושין בכת אחת וקדושין גופייהו ממאי דבכת אחת דלמא בב' כיתי עדים אי בב' כיתי עדים תתייבם ואין בכך כלום

[the reply was] that if he was a priest she is forbidden to him;<span class="x" onmousemove="('comment',' A priest must not marry or continue to live with a divorced woman. ');">²⁶</span> and if she is a forbidden relative, her rival must perform the <i>halizah</i>.<span class="x" onmousemove="('comment',' Git. 78a. ');">²⁷</span> We do not say, however, that were you to rule that she must perform <i>halizah</i> she might also be taken in levirate marriage!<span class="x" onmousemove="('comment',' Which shews that even in the case of divorce no preventive measure has been enacted. ');">²⁸</span>

Maharach Or Zarua Responsa