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<PRE>
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`read columns ...'
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<p>
Read numbers into columns.  These columns have predefined
meanings and names.  For example, `<font color="#82140F"><code>read columns x y</code></font>' instructs Gri
to read data into columns called `<font color="#82140F"><code>x</code></font>' and `<font color="#82140F"><code>y</code></font>'; it is these data
that Gri will use if you tell it to `<font color="#82140F"><code>draw curve</code><