t;
&gt; &gt; But how do you write the value of f at x?  Strictly speaking,
&gt; &gt; that is, according to the rulebook of syntactic substitution,
&gt; &gt; one ought to write either "f(x)" or "f(&lt;x&lt;1&gt;, ..., x&lt;n&gt;&gt;)",
&gt; &gt; and when you go through this ringer for the first time, some
&gt; &gt; professors will actually insist that you preserve this purity
&gt; &gt; of notational discipline, sanctioning "f(x&lt;1&gt;, ..., x&lt;n&gt;)" as
&gt; &gt; a vile abuse of notation.  Of course, th