Always allow at least one extra line of space above subheadings, and preferably below as well. Without this extra space, it is sometimes difficult to distinguish headings from text. A heading must never appear alone at the bottom of a page (a “widow”) without at least two lines of text under it. Also keep in mind the conventional wisdom that a unit cannot be divided into a single part, or “you can’t have an A without a B.” If you have only one second-level heading under a given first-level heading, you should probably incorporate it into the text or, if subdivision is really called for, create another second-level heading. Addition- ally, if you have only one appendix, call it simply Appendix, not Appendix A.