 semantics for macro expansion has been more fully
specified.
</p>
<li><p>Internal definitions are now defined in terms of <tt>letrec*</tt>.
</p>
<li><p>The old notion of program structure and Scheme&#8217;s top-level
environment has been replaced by top-level programs and libraries.
</p>
<li><p>The denotational semantics has been replaced by an operational
semantics based on an earlier semantics for the language of the
&#8220;Revised<sup>5</sup> Report&#8221;&nbsp;[<a href="r6rs-Z-H-21.html#node_bib_14">14