I've stared at the formal syntax, and read it as:
lambda is (lambda <formals> <body>)
<body> is <definition>* <sequence>
<definition>* is
(define <variable> <expression>)
| (define (<variable> <def formals>) <body>)
| (begin <definition>*)so (lambda () (begin (define ...) ... in both forms looks legal to me.
