 columns</code></font>' line, then the new data will be appended to any
existing columnar data; otherwise they will overwrite any existing data.
<p>
As a special case, if the `<font color="#82140F"><code>x</code></font>' column is not indicated
(e.g. `<font color="#82140F"><code>read columns y</code></font>') then Gri creates x-values automatically, in
the sequence 0, 1, 2, etc.
<p>
<ul>
<p>
<li> `<font color="#82140F"><code>read columns x y</code></font>'
Read `<font color="#82140F"><code>x</code></font>' 