Reference for Gittin 52:9

אלא מן האירוסין בשלמא למ"ד משום בת אחותו איכא אלא למ"ד משום פירי ארוסה מי אית לה פירי

If a man says, 'Write a Get for my fiancee, I will divorce her with it after I marry her,' it is no Get. And commenting on this 'Ulla said: What is the reason? Because people may say that her Get came [before] her child.<span class="x" onmousemove="('comment',' I.e., that she was divorced while still only affianced, and that therefore her child was born out of wedlock. ');">⁸</span>

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