For me, a big turning point, in learning anything really, came when I started looking at the bibliography/references. Any text can be considered "introductory",

For me, a big turning point, in learning anything really, came when I started looking at the bibliography/references. Any text can be considered "introductory", and I believe all classes are. If you really want to go deeper, you have to go to the references and study outside class, and no one tells you this.