Location of Question 67.5.2: We haven't defined concrete category yet

<img width="818" alt="Image" src="https://github.com/user-attachments/assets/763e68ab-2d3d-401d-9d89-25187c9ded8a" /> The definition of a concrete category doesn’t appear until Remark 68.2.3, so at the point of Question 67.5.2, the reader hasn’t seen it yet. We should either change the wording of “Verify that” to “Convince yourself that” or move Question 67.5.2 to a later section. What do you think? Personally, I’d suggest weakening the wording in Question 67.5.2 to “Convince yourself that” and then asking for a formal proof again after Remark 68.2.3.