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cbbe75fe67
lca_inner() wasn't prepared for the possibility of getting no inputs. Fix that, and make some cosmetic improvements to the code while at it. Also, I thought the documentation of this function as returning the "longest common prefix" of the paths was entirely misleading; it really returns a path one shorter than the longest common prefix, for the typical definition of "prefix". Don't use that term in the docs, and adjust the examples to clarify what really happens. This has been broken since its beginning, so back-patch to all supported branches. Per report from Hailong Li. Thanks to Pierre Ducroquet for diagnosing and for the initial patch, though I whacked it around some and added test cases. Discussion: https://postgr.es/m/5b0d8e4f-f2a3-1305-d612-e00e35a7be66@qunar.com
677 lines
23 KiB
Text
677 lines
23 KiB
Text
<!-- doc/src/sgml/ltree.sgml -->
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<sect1 id="ltree" xreflabel="ltree">
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<title>ltree</title>
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<indexterm zone="ltree">
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<primary>ltree</primary>
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</indexterm>
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<para>
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This module implements a data type <type>ltree</> for representing
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labels of data stored in a hierarchical tree-like structure.
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Extensive facilities for searching through label trees are provided.
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</para>
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<sect2>
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<title>Definitions</title>
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<para>
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A <firstterm>label</firstterm> is a sequence of alphanumeric characters
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and underscores (for example, in C locale the characters
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<literal>A-Za-z0-9_</> are allowed). Labels must be less than 256 bytes
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long.
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</para>
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<para>
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Examples: <literal>42</>, <literal>Personal_Services</>
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</para>
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<para>
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A <firstterm>label path</firstterm> is a sequence of zero or more
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labels separated by dots, for example <literal>L1.L2.L3</>, representing
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a path from the root of a hierarchical tree to a particular node. The
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length of a label path must be less than 65Kb, but keeping it under 2Kb is
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preferable.
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</para>
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<para>
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Example: <literal>Top.Countries.Europe.Russia</literal>
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</para>
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<para>
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The <filename>ltree</> module provides several data types:
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</para>
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<itemizedlist>
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<listitem>
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<para>
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<type>ltree</type> stores a label path.
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</para>
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</listitem>
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<listitem>
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<para>
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<type>lquery</type> represents a regular-expression-like pattern
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for matching <type>ltree</> values. A simple word matches that
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label within a path. A star symbol (<literal>*</>) matches zero
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or more labels. For example:
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<synopsis>
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foo <lineannotation>Match the exact label path <literal>foo</></lineannotation>
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*.foo.* <lineannotation>Match any label path containing the label <literal>foo</></lineannotation>
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*.foo <lineannotation>Match any label path whose last label is <literal>foo</></lineannotation>
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</synopsis>
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</para>
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<para>
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Star symbols can also be quantified to restrict how many labels
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they can match:
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<synopsis>
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*{<replaceable>n</>} <lineannotation>Match exactly <replaceable>n</> labels</lineannotation>
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*{<replaceable>n</>,} <lineannotation>Match at least <replaceable>n</> labels</lineannotation>
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*{<replaceable>n</>,<replaceable>m</>} <lineannotation>Match at least <replaceable>n</> but not more than <replaceable>m</> labels</lineannotation>
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*{,<replaceable>m</>} <lineannotation>Match at most <replaceable>m</> labels — same as </lineannotation> *{0,<replaceable>m</>}
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</synopsis>
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</para>
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<para>
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There are several modifiers that can be put at the end of a non-star
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label in <type>lquery</> to make it match more than just the exact match:
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<synopsis>
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@ <lineannotation>Match case-insensitively, for example <literal>a@</> matches <literal>A</></lineannotation>
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* <lineannotation>Match any label with this prefix, for example <literal>foo*</> matches <literal>foobar</></lineannotation>
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% <lineannotation>Match initial underscore-separated words</lineannotation>
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</synopsis>
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The behavior of <literal>%</> is a bit complicated. It tries to match
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words rather than the entire label. For example
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<literal>foo_bar%</> matches <literal>foo_bar_baz</> but not
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<literal>foo_barbaz</>. If combined with <literal>*</>, prefix
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matching applies to each word separately, for example
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<literal>foo_bar%*</> matches <literal>foo1_bar2_baz</> but
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not <literal>foo1_br2_baz</>.
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</para>
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<para>
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Also, you can write several possibly-modified labels separated with
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<literal>|</> (OR) to match any of those labels, and you can put
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<literal>!</> (NOT) at the start to match any label that doesn't
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match any of the alternatives.
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</para>
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<para>
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Here's an annotated example of <type>lquery</type>:
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<programlisting>
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Top.*{0,2}.sport*@.!football|tennis.Russ*|Spain
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a. b. c. d. e.
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</programlisting>
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This query will match any label path that:
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</para>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>
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begins with the label <literal>Top</literal>
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</para>
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</listitem>
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<listitem>
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<para>
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and next has zero to two labels before
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</para>
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</listitem>
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<listitem>
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<para>
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a label beginning with the case-insensitive prefix <literal>sport</literal>
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</para>
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</listitem>
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<listitem>
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<para>
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then a label not matching <literal>football</literal> nor
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<literal>tennis</literal>
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</para>
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</listitem>
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<listitem>
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<para>
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and then ends with a label beginning with <literal>Russ</literal> or
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exactly matching <literal>Spain</literal>.
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</para>
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</listitem>
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</orderedlist>
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</listitem>
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<listitem>
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<para><type>ltxtquery</type> represents a full-text-search-like
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pattern for matching <type>ltree</> values. An
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<type>ltxtquery</type> value contains words, possibly with the
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modifiers <literal>@</>, <literal>*</>, <literal>%</> at the end;
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the modifiers have the same meanings as in <type>lquery</>.
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Words can be combined with <literal>&</> (AND),
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<literal>|</> (OR), <literal>!</> (NOT), and parentheses.
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The key difference from
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<type>lquery</> is that <type>ltxtquery</type> matches words without
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regard to their position in the label path.
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</para>
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<para>
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Here's an example <type>ltxtquery</type>:
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<programlisting>
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Europe & Russia*@ & !Transportation
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</programlisting>
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This will match paths that contain the label <literal>Europe</literal> and
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any label beginning with <literal>Russia</literal> (case-insensitive),
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but not paths containing the label <literal>Transportation</literal>.
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The location of these words within the path is not important.
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Also, when <literal>%</> is used, the word can be matched to any
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underscore-separated word within a label, regardless of position.
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</para>
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</listitem>
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</itemizedlist>
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<para>
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Note: <type>ltxtquery</> allows whitespace between symbols, but
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<type>ltree</> and <type>lquery</> do not.
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</para>
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</sect2>
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<sect2>
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<title>Operators and Functions</title>
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<para>
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Type <type>ltree</> has the usual comparison operators
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<literal>=</>, <literal><></literal>,
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<literal><</>, <literal>></>, <literal><=</>, <literal>>=</>.
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Comparison sorts in the order of a tree traversal, with the children
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of a node sorted by label text. In addition, the specialized
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operators shown in <xref linkend="ltree-op-table"> are available.
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</para>
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<table id="ltree-op-table">
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<title><type>ltree</> Operators</title>
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<tgroup cols="3">
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<thead>
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<row>
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<entry>Operator</entry>
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<entry>Returns</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><type>ltree</> <literal>@></> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>is left argument an ancestor of right (or equal)?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal><@</> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>is left argument a descendant of right (or equal)?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>~</> <type>lquery</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>lquery</> <literal>~</> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>?</> <type>lquery[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match any <type>lquery</> in array?</entry>
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</row>
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<row>
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<entry><type>lquery[]</> <literal>?</> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match any <type>lquery</> in array?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>@</> <type>ltxtquery</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match <type>ltxtquery</>?</entry>
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</row>
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<row>
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<entry><type>ltxtquery</> <literal>@</> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> match <type>ltxtquery</>?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>||</> <type>ltree</></entry>
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<entry><type>ltree</type></entry>
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<entry>concatenate <type>ltree</> paths</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>||</> <type>text</></entry>
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<entry><type>ltree</type></entry>
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<entry>convert text to <type>ltree</> and concatenate</entry>
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</row>
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<row>
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<entry><type>text</> <literal>||</> <type>ltree</></entry>
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<entry><type>ltree</type></entry>
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<entry>convert text to <type>ltree</> and concatenate</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>@></> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain an ancestor of <type>ltree</>?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal><@</> <type>ltree[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain an ancestor of <type>ltree</>?</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal><@</> <type>ltree</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain a descendant of <type>ltree</>?</entry>
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</row>
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<row>
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<entry><type>ltree</> <literal>@></> <type>ltree[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain a descendant of <type>ltree</>?</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>~</> <type>lquery</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain any path matching <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>lquery</> <literal>~</> <type>ltree[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain any path matching <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>?</> <type>lquery[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> array contain any path matching any <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>lquery[]</> <literal>?</> <type>ltree[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does <type>ltree</> array contain any path matching any <type>lquery</>?</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>@</> <type>ltxtquery</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain any path matching <type>ltxtquery</>?</entry>
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</row>
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<row>
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<entry><type>ltxtquery</> <literal>@</> <type>ltree[]</></entry>
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<entry><type>boolean</type></entry>
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<entry>does array contain any path matching <type>ltxtquery</>?</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>?@></> <type>ltree</></entry>
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<entry><type>ltree</type></entry>
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<entry>first array entry that is an ancestor of <type>ltree</>; NULL if none</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>?<@</> <type>ltree</></entry>
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<entry><type>ltree</type></entry>
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<entry>first array entry that is a descendant of <type>ltree</>; NULL if none</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>?~</> <type>lquery</></entry>
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<entry><type>ltree</type></entry>
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<entry>first array entry that matches <type>lquery</>; NULL if none</entry>
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</row>
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<row>
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<entry><type>ltree[]</> <literal>?@</> <type>ltxtquery</></entry>
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<entry><type>ltree</type></entry>
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<entry>first array entry that matches <type>ltxtquery</>; NULL if none</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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The operators <literal><@</literal>, <literal>@></literal>,
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<literal>@</literal> and <literal>~</literal> have analogues
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<literal>^<@</>, <literal>^@></>, <literal>^@</>,
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<literal>^~</literal>, which are the same except they do not use
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indexes. These are useful only for testing purposes.
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</para>
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<para>
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The available functions are shown in <xref linkend="ltree-func-table">.
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</para>
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<table id="ltree-func-table">
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<title><type>ltree</> Functions</title>
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<tgroup cols="5">
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<thead>
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<row>
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<entry>Function</entry>
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<entry>Return Type</entry>
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<entry>Description</entry>
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<entry>Example</entry>
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<entry>Result</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry><function>subltree(ltree, int start, int end)</function><indexterm><primary>subltree</primary></indexterm></entry>
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<entry><type>ltree</type></entry>
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<entry>subpath of <type>ltree</> from position <parameter>start</> to
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position <parameter>end</>-1 (counting from 0)</entry>
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<entry><literal>subltree('Top.Child1.Child2',1,2)</literal></entry>
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<entry><literal>Child1</literal></entry>
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</row>
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<row>
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<entry><function>subpath(ltree, int offset, int len)</function><indexterm><primary>subpath</primary></indexterm></entry>
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<entry><type>ltree</type></entry>
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<entry>subpath of <type>ltree</> starting at position
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<parameter>offset</>, length <parameter>len</>.
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If <parameter>offset</> is negative, subpath starts that far from the
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end of the path. If <parameter>len</> is negative, leaves that many
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labels off the end of the path.</entry>
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<entry><literal>subpath('Top.Child1.Child2',0,2)</literal></entry>
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<entry><literal>Top.Child1</literal></entry>
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</row>
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<row>
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<entry><function>subpath(ltree, int offset)</function></entry>
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<entry><type>ltree</type></entry>
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<entry>subpath of <type>ltree</> starting at position
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<parameter>offset</>, extending to end of path.
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If <parameter>offset</> is negative, subpath starts that far from the
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end of the path.</entry>
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<entry><literal>subpath('Top.Child1.Child2',1)</literal></entry>
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<entry><literal>Child1.Child2</literal></entry>
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</row>
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<row>
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<entry><function>nlevel(ltree)</function><indexterm><primary>nlevel</primary></indexterm></entry>
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<entry><type>integer</type></entry>
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<entry>number of labels in path</entry>
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<entry><literal>nlevel('Top.Child1.Child2')</literal></entry>
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<entry><literal>3</literal></entry>
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</row>
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<row>
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<entry><function>index(ltree a, ltree b)</function><indexterm><primary>index</primary></indexterm></entry>
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<entry><type>integer</type></entry>
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<entry>position of first occurrence of <parameter>b</> in
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<parameter>a</>; -1 if not found</entry>
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<entry><literal>index('0.1.2.3.5.4.5.6.8.5.6.8','5.6')</literal></entry>
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<entry><literal>6</literal></entry>
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</row>
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<row>
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<entry><function>index(ltree a, ltree b, int offset)</function></entry>
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<entry><type>integer</type></entry>
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<entry>position of first occurrence of <parameter>b</> in
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<parameter>a</>, searching starting at <parameter>offset</>;
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negative <parameter>offset</> means start <parameter>-offset</>
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labels from the end of the path</entry>
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<entry><literal>index('0.1.2.3.5.4.5.6.8.5.6.8','5.6',-4)</literal></entry>
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<entry><literal>9</literal></entry>
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</row>
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<row>
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<entry><function>text2ltree(text)</function><indexterm><primary>text2ltree</primary></indexterm></entry>
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<entry><type>ltree</type></entry>
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<entry>cast <type>text</> to <type>ltree</></entry>
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<entry><literal></literal></entry>
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<entry><literal></literal></entry>
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</row>
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<row>
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<entry><function>ltree2text(ltree)</function><indexterm><primary>ltree2text</primary></indexterm></entry>
|
|
<entry><type>text</type></entry>
|
|
<entry>cast <type>ltree</> to <type>text</></entry>
|
|
<entry><literal></literal></entry>
|
|
<entry><literal></literal></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><function>lca(ltree, ltree, ...)</function><indexterm><primary>lca</primary></indexterm></entry>
|
|
<entry><type>ltree</type></entry>
|
|
<entry>longest common ancestor of paths
|
|
(up to 8 arguments supported)</entry>
|
|
<entry><literal>lca('1.2.3','1.2.3.4.5.6')</literal></entry>
|
|
<entry><literal>1.2</literal></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry><function>lca(ltree[])</function></entry>
|
|
<entry><type>ltree</type></entry>
|
|
<entry>longest common ancestor of paths in array</entry>
|
|
<entry><literal>lca(array['1.2.3'::ltree,'1.2.3.4'])</literal></entry>
|
|
<entry><literal>1.2</literal></entry>
|
|
</row>
|
|
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Indexes</title>
|
|
<para>
|
|
<filename>ltree</> supports several types of indexes that can speed
|
|
up the indicated operators:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>
|
|
B-tree index over <type>ltree</>:
|
|
<literal><</>, <literal><=</>, <literal>=</>,
|
|
<literal>>=</>, <literal>></literal>
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
GiST index over <type>ltree</>:
|
|
<literal><</>, <literal><=</>, <literal>=</>,
|
|
<literal>>=</>, <literal>></>,
|
|
<literal>@></>, <literal><@</>,
|
|
<literal>@</>, <literal>~</>, <literal>?</literal>
|
|
</para>
|
|
<para>
|
|
Example of creating such an index:
|
|
</para>
|
|
<programlisting>
|
|
CREATE INDEX path_gist_idx ON test USING GIST (path);
|
|
</programlisting>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
GiST index over <type>ltree[]</>:
|
|
<literal>ltree[] <@ ltree</>, <literal>ltree @> ltree[]</>,
|
|
<literal>@</>, <literal>~</>, <literal>?</literal>
|
|
</para>
|
|
<para>
|
|
Example of creating such an index:
|
|
</para>
|
|
<programlisting>
|
|
CREATE INDEX path_gist_idx ON test USING GIST (array_path);
|
|
</programlisting>
|
|
<para>
|
|
Note: This index type is lossy.
|
|
</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Example</title>
|
|
|
|
<para>
|
|
This example uses the following data (also available in file
|
|
<filename>contrib/ltree/ltreetest.sql</> in the source distribution):
|
|
</para>
|
|
|
|
<programlisting>
|
|
CREATE TABLE test (path ltree);
|
|
INSERT INTO test VALUES ('Top');
|
|
INSERT INTO test VALUES ('Top.Science');
|
|
INSERT INTO test VALUES ('Top.Science.Astronomy');
|
|
INSERT INTO test VALUES ('Top.Science.Astronomy.Astrophysics');
|
|
INSERT INTO test VALUES ('Top.Science.Astronomy.Cosmology');
|
|
INSERT INTO test VALUES ('Top.Hobbies');
|
|
INSERT INTO test VALUES ('Top.Hobbies.Amateurs_Astronomy');
|
|
INSERT INTO test VALUES ('Top.Collections');
|
|
INSERT INTO test VALUES ('Top.Collections.Pictures');
|
|
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy');
|
|
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Stars');
|
|
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Galaxies');
|
|
INSERT INTO test VALUES ('Top.Collections.Pictures.Astronomy.Astronauts');
|
|
CREATE INDEX path_gist_idx ON test USING gist(path);
|
|
CREATE INDEX path_idx ON test USING btree(path);
|
|
</programlisting>
|
|
|
|
<para>
|
|
Now, we have a table <structname>test</> populated with data describing
|
|
the hierarchy shown below:
|
|
</para>
|
|
|
|
<literallayout class="monospaced">
|
|
Top
|
|
/ | \
|
|
Science Hobbies Collections
|
|
/ | \
|
|
Astronomy Amateurs_Astronomy Pictures
|
|
/ \ |
|
|
Astrophysics Cosmology Astronomy
|
|
/ | \
|
|
Galaxies Stars Astronauts
|
|
</literallayout>
|
|
|
|
<para>
|
|
We can do inheritance:
|
|
<screen>
|
|
ltreetest=> SELECT path FROM test WHERE path <@ 'Top.Science';
|
|
path
|
|
------------------------------------
|
|
Top.Science
|
|
Top.Science.Astronomy
|
|
Top.Science.Astronomy.Astrophysics
|
|
Top.Science.Astronomy.Cosmology
|
|
(4 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Here are some examples of path matching:
|
|
<screen>
|
|
ltreetest=> SELECT path FROM test WHERE path ~ '*.Astronomy.*';
|
|
path
|
|
-----------------------------------------------
|
|
Top.Science.Astronomy
|
|
Top.Science.Astronomy.Astrophysics
|
|
Top.Science.Astronomy.Cosmology
|
|
Top.Collections.Pictures.Astronomy
|
|
Top.Collections.Pictures.Astronomy.Stars
|
|
Top.Collections.Pictures.Astronomy.Galaxies
|
|
Top.Collections.Pictures.Astronomy.Astronauts
|
|
(7 rows)
|
|
|
|
ltreetest=> SELECT path FROM test WHERE path ~ '*.!pictures@.*.Astronomy.*';
|
|
path
|
|
------------------------------------
|
|
Top.Science.Astronomy
|
|
Top.Science.Astronomy.Astrophysics
|
|
Top.Science.Astronomy.Cosmology
|
|
(3 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Here are some examples of full text search:
|
|
<screen>
|
|
ltreetest=> SELECT path FROM test WHERE path @ 'Astro*% & !pictures@';
|
|
path
|
|
------------------------------------
|
|
Top.Science.Astronomy
|
|
Top.Science.Astronomy.Astrophysics
|
|
Top.Science.Astronomy.Cosmology
|
|
Top.Hobbies.Amateurs_Astronomy
|
|
(4 rows)
|
|
|
|
ltreetest=> SELECT path FROM test WHERE path @ 'Astro* & !pictures@';
|
|
path
|
|
------------------------------------
|
|
Top.Science.Astronomy
|
|
Top.Science.Astronomy.Astrophysics
|
|
Top.Science.Astronomy.Cosmology
|
|
(3 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Path construction using functions:
|
|
<screen>
|
|
ltreetest=> SELECT subpath(path,0,2)||'Space'||subpath(path,2) FROM test WHERE path <@ 'Top.Science.Astronomy';
|
|
?column?
|
|
------------------------------------------
|
|
Top.Science.Space.Astronomy
|
|
Top.Science.Space.Astronomy.Astrophysics
|
|
Top.Science.Space.Astronomy.Cosmology
|
|
(3 rows)
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
We could simplify this by creating a SQL function that inserts a label
|
|
at a specified position in a path:
|
|
<screen>
|
|
CREATE FUNCTION ins_label(ltree, int, text) RETURNS ltree
|
|
AS 'select subpath($1,0,$2) || $3 || subpath($1,$2);'
|
|
LANGUAGE SQL IMMUTABLE;
|
|
|
|
ltreetest=> SELECT ins_label(path,2,'Space') FROM test WHERE path <@ 'Top.Science.Astronomy';
|
|
ins_label
|
|
------------------------------------------
|
|
Top.Science.Space.Astronomy
|
|
Top.Science.Space.Astronomy.Astrophysics
|
|
Top.Science.Space.Astronomy.Cosmology
|
|
(3 rows)
|
|
</screen>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2>
|
|
<title>Authors</title>
|
|
|
|
<para>
|
|
All work was done by Teodor Sigaev (<email>teodor@stack.net</email>) and
|
|
Oleg Bartunov (<email>oleg@sai.msu.su</email>). See
|
|
<ulink url="http://www.sai.msu.su/~megera/postgres/gist/"></ulink> for
|
|
additional information. Authors would like to thank Eugeny Rodichev for
|
|
helpful discussions. Comments and bug reports are welcome.
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|