My students have sometimes lacked enough background in some of the foundations needed for the material I teach and work with. Rather than having them buy extra textbooks for (usually) a small amount of material, I gradually accumulated these pages. In later years I also added pages for analogous areas I was learning and using myself.
I would like to thank the many students (and other readers) whose suggestions and comments have improved these pages markedly. All remaining flaws are due to the author. Please contact me if you find an error.