The back matter solutions appendix requests every <answer>, and only <answer>, of all types of exercises: inline, divisional, worksheet, reading questions, and projects. Now, as observed by Bruce Yoshiwara, it gets a bit tedious to see the “Answer” heading over and over in print, when every entry has that heading. So we squelch it for you in print/PDF output. (For HTML output we use knowls and need to have something to click on. But perhaps for EPUB we should be more careful?) Note that you might want to use a <title>, or an <introduction>, that explains which component of the exercises is being displayed, so there is no confusion.
4An Interesting Corollary 4.2A Pedagogical Note about Subsection 4.1 4.2.3Advice