I checked a chapter 17 to see what was up with that.
Exercise 17.6.1. Develop the function merge. It consumes two lists of numbers, sorted in ascending order. It produces a single sorted list of numbers that contains all the numbers on both inputs lists (and nothing else). A number occurs in the output as many times as it occurs on the two input lists together.
Really, after seventeen chapters I thought the book would get to something more complicated than merging two ordered lists. The other exercises in the chapter aren't much harder. This is almost halfway through the book.