n referring to the elements of R and mappings from R to R,
&gt; &gt; one naturally uses notations like "x in R",  "f : R -&gt; R",
&gt; &gt; and the value of f at x is written "f(x)".  So far, so good.
&gt; &gt;
&gt; &gt; When one finally arrives at the n-dimensional case, it is
&gt; &gt; usual to write things like "x = &lt;x&lt;1&gt;, ..., x&lt;n&gt;&gt;", using
&gt; &gt; either the single letter or the coordinate list, depending
&gt; &gt; on whichever is convenient at a given moment of discussion.
&gt; &g