olumn is used for contouring.
<p>
<li> `<font color="#82140F"><code>read columns x y u v</code></font>'
Read `<font color="#82140F"><code>x</code></font>' and `<font color="#82140F"><code>y</code></font>' in first two columns, and the ``arrow'' data
`<font color="#82140F"><code>u</code></font>' and `<font color="#82140F"><code>v</code></font>' as third and fourth columns.
<p>
<li> `<font color="#82140F"><code>read columns .rows. x y</code></font>'
Read `<font color="#82140F"><code>.rows.</code></font>' rows