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<dt><u>Function:</u> <b>read_nested_list</b><i> (<var>S</var>, <var>separator_flag</var>)</i>
<a name="IDX2518"></a>
</dt>
<dd><p>Reads the source <var>S</var> and returns its entire content as a nested list.
The source <var>S</var> may be a file name or a stream.
</p>
<p><code>read_nested_list</code> returns a list which has a sublist for each
line of input. Lines need not have the same numbers of elements.
Empty lines are <i>not</i> ignored: an empty line yields an empty sublist.
</p>
<p>The recognized 