### 13.2 Lambda Expressions

A lambda expression is a function object written in Lisp. Here is
an example:

(lambda (x)
"Return the hyperbolic cosine of X."
(* 0.5 (+ (exp x) (exp (- x)))))

In Emacs Lisp, such a list is a valid expression which evaluates to
a function object.

A lambda expression, by itself, has no name; it is an *anonymous
function*. Although lambda expressions can be used this way
(see Anonymous Functions), they are more commonly associated with
symbols to make *named functions* (see Naming a Function).
Before going into these details, the following subsections describe
the components of a lambda expression and what they do.