Writing GNU Emacs Extensinos Chapter 2 - Simple New Commands

interactive takes one argument: a trings of code letters, one code letter per argument being described. The code letter p means, "if there is a prefix argument, interpret it as a number, and if there is no prefix argument, interpret that as the number 1"

Writing GNU Emacs Extensinos Chapter 1 - Customizing Emacs

In Lisp, functions are named with symbols. Smbols are like function names or varible names in other language, althought Lisp allows a wider variety of characters in symbols than most languages allow in their variable names