I have the Princeton Companion to Mathematics, which I'm enjoying overall. However, right now it's a lot more useful to me for expanding on topics I'm already somewhat familiar and less useful for understanding completely new ones. The problem is that the articles in some of the key sections are in ABC order, which is not the most logical order for learning. The articles cross-reference each other, but I was hoping there might be a more efficient method to get introduced to a new area (for example, the Axiom of Choice is the first article in Section III while the ZF axioms are last). Does anyone have any suggestions for which articles to read and in which order to start learning about specific subjects or at least a logical grouping of some of the articles? Thanks!