Reference for Bava Kamma 133:2

רבי זירא אמר שינוי החוזר לברייתו בשינוי השם לא הוי שינוי

these are the casings: 'and the thick planks'; these are the beams.<span class="x" onmousemove="('comment',' Hence after it became part of the ceiling it is still called beam. ');">³</span> R. Zera said: A change which can revert to its original state is, in the case of a change in name, not considered a change.<span class="x" onmousemove="('comment',' A beam by becoming part of a ceiling did not therefore really undergo a change in name, as the beam could be taken out and thus revert to its original state. ');">⁴</span>

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