Programs and definitions (Revised(5) Scheme)

<program> --> <command or definition>*
<command or definition> --> <command>
    | <definition>
    | <syntax definition>
    | (begin <command or definition>+)
<definition> --> (define <variable> <expression>)
      | (define (<variable> <def formals>) <body>)
      | (begin <definition>*)
<def formals> --> <variable>*
      | <variable>* . <variable>
<syntax definition> -->
     (define-syntax <keyword> <transformer spec>)

7.1.6 Programs and definitions