Definitions

Definitions are valid in some, but not all, contexts where expressions are allowed. They are valid only at the top level of a program and, in some implementations, at the beginning of a body. definition

A definition should have one of the following forms:define

(define variable expression)
This syntax is essential.
(define (variable formals) body)
This syntax is not essential. Formals should be either a sequence of zero or more variables, or a sequence of one or more variables followed by a space-delimited period and another variable (as in a lambda expression). This form is equivalent to
$\begin{scheme} (define \hyper{variable} (lambda (\hyper{formals}) \hyper{body}))\rm .% \end{scheme}$
(define (variable . formal) body)
This syntax is not essential. Formal should be a single variable. This form is equivalent to
$\begin{scheme} (define \hyper{variable} (lambda \hyper{formal} \hyper{body}))\rm .% \end{scheme}$
(begin definition )
This syntax is essential. This form is equivalent to the set of definitions that form the body of the begin.

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