I am not sure if this has been fixed in the actual book, but exercise 1.6.13 in the draft is not true. I think it should ask you to prove that the inequality in exercise 1.6.12 is an equality.

*[Thanks for the correction – T.]*

(btw I am not the Anony that posted the previous message.)

*[Ah, got it. It turns out that this error was already corrected in the published version, which is why I couldn’t find it. -T.]*

*[I was unable to locate this typo. Could you provide a page number please? Thanks – T.]*