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<title>pcrebuild specification</title> |
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> |
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This HTML document has been generated automatically from the original man page. |
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If there is any nonsense in it, please consult the man page, in case the |
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conversion went wrong.<br> |
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<ul> |
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<li><a name="TOC1" href="#SEC1">PCRE BUILD-TIME OPTIONS</a> |
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<li><a name="TOC2" href="#SEC2">UTF-8 SUPPORT</a> |
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<li><a name="TOC3" href="#SEC3">CODE VALUE OF NEWLINE</a> |
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<li><a name="TOC4" href="#SEC4">BUILDING SHARED AND STATIC LIBRARIES</a> |
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<li><a name="TOC5" href="#SEC5">POSIX MALLOC USAGE</a> |
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<li><a name="TOC6" href="#SEC6">LIMITING PCRE RESOURCE USAGE</a> |
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<li><a name="TOC7" href="#SEC7">HANDLING VERY LARGE PATTERNS</a> |
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<li><a name="TOC8" href="#SEC8">AVOIDING EXCESSIVE STACK USAGE</a> |
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<li><a name="TOC9" href="#SEC9">USING EBCDIC CODE</a> |
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</ul> |
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<br><a name="SEC1" href="#TOC1">PCRE BUILD-TIME OPTIONS</a><br> |
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<P> |
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This document describes the optional features of PCRE that can be selected when |
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the library is compiled. They are all selected, or deselected, by providing |
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options to the <b>configure</b> script which is run before the <b>make</b> |
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command. The complete list of options for <b>configure</b> (which includes the |
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standard ones such as the selection of the installation directory) can be |
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obtained by running |
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</P> |
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<P> |
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<pre> |
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./configure --help |
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</PRE> |
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</P> |
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<P> |
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The following sections describe certain options whose names begin with --enable |
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or --disable. These settings specify changes to the defaults for the |
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<b>configure</b> command. Because of the way that <b>configure</b> works, |
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--enable and --disable always come in pairs, so the complementary option always |
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exists as well, but as it specifies the default, it is not described. |
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</P> |
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<br><a name="SEC2" href="#TOC1">UTF-8 SUPPORT</a><br> |
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<P> |
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To build PCRE with support for UTF-8 character strings, add |
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</P> |
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<P> |
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<pre> |
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--enable-utf8 |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. Of itself, this does not make PCRE treat |
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strings as UTF-8. As well as compiling PCRE with this option, you also have |
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have to set the PCRE_UTF8 option when you call the <b>pcre_compile()</b> |
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function. |
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</P> |
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<br><a name="SEC3" href="#TOC1">CODE VALUE OF NEWLINE</a><br> |
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<P> |
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By default, PCRE treats character 10 (linefeed) as the newline character. This |
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is the normal newline character on Unix-like systems. You can compile PCRE to |
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use character 13 (carriage return) instead by adding |
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</P> |
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<P> |
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<pre> |
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--enable-newline-is-cr |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. For completeness there is also a |
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--enable-newline-is-lf option, which explicitly specifies linefeed as the |
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newline character. |
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</P> |
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<br><a name="SEC4" href="#TOC1">BUILDING SHARED AND STATIC LIBRARIES</a><br> |
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<P> |
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The PCRE building process uses <b>libtool</b> to build both shared and static |
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Unix libraries by default. You can suppress one of these by adding one of |
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</P> |
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<P> |
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<pre> |
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--disable-shared |
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--disable-static |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command, as required. |
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</P> |
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<br><a name="SEC5" href="#TOC1">POSIX MALLOC USAGE</a><br> |
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<P> |
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When PCRE is called through the POSIX interface (see the <b>pcreposix</b> |
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documentation), additional working storage is required for holding the pointers |
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to capturing substrings because PCRE requires three integers per substring, |
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whereas the POSIX interface provides only two. If the number of expected |
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substrings is small, the wrapper function uses space on the stack, because this |
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is faster than using <b>malloc()</b> for each call. The default threshold above |
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which the stack is no longer used is 10; it can be changed by adding a setting |
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such as |
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</P> |
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<P> |
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<pre> |
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--with-posix-malloc-threshold=20 |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. |
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</P> |
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<br><a name="SEC6" href="#TOC1">LIMITING PCRE RESOURCE USAGE</a><br> |
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<P> |
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Internally, PCRE has a function called <b>match()</b> which it calls repeatedly |
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(possibly recursively) when performing a matching operation. By limiting the |
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number of times this function may be called, a limit can be placed on the |
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resources used by a single call to <b>pcre_exec()</b>. The limit can be changed |
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at run time, as described in the <b>pcreapi</b> documentation. The default is 10 |
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million, but this can be changed by adding a setting such as |
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</P> |
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<P> |
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<pre> |
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--with-match-limit=500000 |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. |
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</P> |
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<br><a name="SEC7" href="#TOC1">HANDLING VERY LARGE PATTERNS</a><br> |
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<P> |
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Within a compiled pattern, offset values are used to point from one part to |
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another (for example, from an opening parenthesis to an alternation |
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metacharacter). By default two-byte values are used for these offsets, leading |
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to a maximum size for a compiled pattern of around 64K. This is sufficient to |
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handle all but the most gigantic patterns. Nevertheless, some people do want to |
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process enormous patterns, so it is possible to compile PCRE to use three-byte |
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or four-byte offsets by adding a setting such as |
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</P> |
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<P> |
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<pre> |
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--with-link-size=3 |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. The value given must be 2, 3, or 4. Using |
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longer offsets slows down the operation of PCRE because it has to load |
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additional bytes when handling them. |
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</P> |
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<P> |
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If you build PCRE with an increased link size, test 2 (and test 5 if you are |
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using UTF-8) will fail. Part of the output of these tests is a representation |
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of the compiled pattern, and this changes with the link size. |
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</P> |
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<br><a name="SEC8" href="#TOC1">AVOIDING EXCESSIVE STACK USAGE</a><br> |
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<P> |
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PCRE implements backtracking while matching by making recursive calls to an |
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internal function called <b>match()</b>. In environments where the size of the |
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stack is limited, this can severely limit PCRE's operation. (The Unix |
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environment does not usually suffer from this problem.) An alternative approach |
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that uses memory from the heap to remember data, instead of using recursive |
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function calls, has been implemented to work round this problem. If you want to |
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build a version of PCRE that works this way, add |
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</P> |
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<P> |
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<pre> |
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--disable-stack-for-recursion |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. With this configuration, PCRE will use the |
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<b>pcre_stack_malloc</b> and <b>pcre_stack_free</b> variables to call memory |
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management functions. Separate functions are provided because the usage is very |
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predictable: the block sizes requested are always the same, and the blocks are |
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always freed in reverse order. A calling program might be able to implement |
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optimized functions that perform better than the standard <b>malloc()</b> and |
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<b>free()</b> functions. PCRE runs noticeably more slowly when built in this |
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way. |
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</P> |
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<br><a name="SEC9" href="#TOC1">USING EBCDIC CODE</a><br> |
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<P> |
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PCRE assumes by default that it will run in an environment where the character |
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code is ASCII (or UTF-8, which is a superset of ASCII). PCRE can, however, be |
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compiled to run in an EBCDIC environment by adding |
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</P> |
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<P> |
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<pre> |
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--enable-ebcdic |
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</PRE> |
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</P> |
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<P> |
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to the <b>configure</b> command. |
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</P> |
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<P> |
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Last updated: 09 December 2003 |
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<br> |
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Copyright © 1997-2003 University of Cambridge. |
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