9.9: The begin (and end) functions do not always return a (non-const) iterator type.

[xjay73]

The type returned by begin and end depends on the const-ness of the object calling it. If the calling object is const, then begin/end will return a const_iterator. If the calling object is not const, then begin/end will return a (non-const) iterator.

(Your answer for exercise 9.10 reflects this correctly, but it is not made clear in the answer for this exercise.)