For <URL:http://docs.python.org/lib/types-set.html>, append the following new sentence to the 2nd paragraph.

    Iteration over a set returns elements in an indeterminate order, which generally depends on factors outside the scope of the containing program.

*Justification:* users should not be expected to understand without being told that iteration order depends on factors outside the scope of the containing program. (Additionally, unlike the documentation for dictionaries, the documentation for sets fails to give a serious warning not to rely on iteration order.)