re allowed, but not required, to
recognize that some non-tail calls, such as the call to <tt>h</tt>
above, can be evaluated as though they were tail calls.
In the example above, the <tt>let</tt> expression could be compiled
as a tail call to <tt>h</tt>. (The possibility of <tt>h</tt> returning
an unexpected number of values can be ignored, because in that
case the effect of the <tt>let</tt> is explicitly unspecified and
implementation-dependent.)
</blockquote>
<p>
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