#### 7.1.6 Programs and definitions

    <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>)