One easy way to get started at programming is to examine some typical
interactions with an interpreter for the Scheme dialect of Lisp.
Imagine that you are sitting at a computer terminal. You type an
expression, and the interpreter responds by displaying the result of
its evaluating that expression.
One kind of primitive expression you might type is a number. (More
precisely, the expression that you type consists of the numerals that
represent the number in base 10.) If you present Lisp with
a number
