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Declares NAME to be an interface that provides the definitions DEFINITION .... DEFINITION should be a value definition of the form

 (define NAME [VALUE])

or

 (define (NAME VAR ...) [BODY ...])

The values and bodies of the given definitions are optional and default to (void) (for value definitions) or a procedure that signals a runtime error (for procedure definitions). If a value/body is given, it provides a default for later implementations of this interface (see below).