Instead of this evaluation notation:<p><pre><code>    (list (list 1 2) nil)
    -&gt; (list (1 2) nil)
    -&gt; (list (1 2) ())
    -&gt; ((1 2) ())
</code></pre>
we write for example:<p><pre><code>    (list (list 1 2) nil)
    -&gt; (list {(1 2)} nil)
    -&gt; (list {(1 2)} {()})
    -&gt; {((1 2) ())}
</code></pre>
Use curly brackets to identify which arguments have been evaluated to values.<p>See for example:<p><a href="http:&#x2F;&#x2F;www.cs.uml.edu&#x2F;~dimock&#x2F;courses&#x2F;opl&#x2F;Handouts&#x2F;TheSubstitutionModel.pdf" rel="nofollow">http:&#x2F;&#x2F;www.cs.uml.edu&#x2F;~dimock&#x2F;courses&#x2F;opl&#x2F;Handouts&#x2F;TheSubsti...</a>