<type>ltree</type>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>ltree2text</primary></indexterm>
        <function>ltree2text</function> ( <type>ltree</type> )
        <returnvalue>text</returnvalue>
       </para>
       <para>
        Casts <type>ltree</type> to <type>text</type>.
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <indexterm><primary>lca</primary></indexterm>
        <function>lca</function> ( <type>ltree</type> <optional>, <type>ltree</type> <optional>, ... </optional></optional> )
        <returnvalue>ltree</returnvalue>
       </para>
       <para>
        Computes longest common ancestor of paths
        (up to 8 arguments are supported).
       </para>
       <para>
        <literal>lca('1.2.3', '1.2.3.4.5.6')</literal>
        <returnvalue>1.2</returnvalue>
       </para></entry>
      </row>

      <row>
       <entry role="func_table_entry"><para role="func_signature">
        <function>lca</function> ( <type>ltree[]</type> )
        <returnvalue>ltree</returnvalue>
       </para>
       <para>
        Computes longest common ancestor of paths in array.
       </para>
       <para>
        <literal>lca(array['1.2.3'::ltree,'1.2.3.4'])</literal>
        <returnvalue>1.2</returnvalue>
       </para></entry>
      </row>
     </tbody>
    </tgroup>
  </table>
 </sect2>

 <sect2 id="ltree-indexes">
  <title>Indexes</title>
  <para>
   <filename>ltree</filename> supports several types of indexes that can speed
   up the indicated operators:
  </para>

  <itemizedlist>
   <listitem>
    <para>
     B-tree index over <type>ltree</type>:
     <literal>&lt;</literal>, <literal>&lt;=</literal>, <literal>=</literal>,
     <literal>&gt;=</literal>, <literal>&gt;</literal>
    </para>
   </listitem>
   <listitem>
    <para>
     Hash index over <type>ltree</type>:
     <literal>=</literal>
    </para>
   </listitem>

   <listitem>
    <para>
     GiST index over <type>ltree</type> (<literal>gist_ltree_ops</literal>
     opclass):
     <literal>&lt;</literal>, <literal>&lt;=</literal>, <literal>=</literal>,
     <literal>&gt;=</literal>, <literal>&gt;</literal>,
     <literal>@&gt;</literal>, <literal>&lt;@</literal>,
     <literal>@</literal>, <literal>~</literal>, <literal>?</literal>
    </para>
    <para>
     <literal>gist_ltree_ops</literal> GiST opclass approximates a set of
     path labels as a bitmap signature.  Its optional integer parameter
     <literal>siglen</literal> determines the
     signature length in bytes.  The default signature length is 8 bytes.
     The length must be a positive multiple of <type>int</type> alignment
     (4 bytes on most machines)) up to 2024.  Longer
     signatures lead to a more precise search (scanning a smaller fraction of the index and
     fewer heap pages), at the cost of a larger index.
    </para>
    <para>
     Example of creating such an index with the default signature length of 8 bytes:
    </para>
<programlisting>
CREATE INDEX path_gist_idx ON test USING GIST (path);
</programlisting>
    <para>
     Example of creating such an index with a signature length of 100 bytes:
    </para>
<programlisting>
CREATE INDEX path_gist_idx ON test USING GIST (path gist_ltree_ops(siglen=100));
</programlisting>
   </listitem>
   <listitem>
    <para>
     GiST index over <type>ltree[]</type> (<literal>gist__ltree_ops</literal>
     opclass):
     <literal>ltree[] &lt;@ ltree</literal>, <literal>ltree @&gt; ltree[]</literal>,
     <literal>@</literal>, <literal>~</literal>, <literal>?</literal>
    </para>
    <para>
     <literal>gist__ltree_ops</literal> GiST opclass works similarly to
     <literal>gist_ltree_ops</literal> and also takes signature length as
     a parameter.  The default value of <literal>siglen</literal> in
      <literal>gist__ltree_ops</literal> is 28 bytes.
    </para>
    <para>