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200 lines
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>R6RS Libraries (Guile Reference Manual)</title>
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<meta name="description" content="R6RS Libraries (Guile Reference Manual)">
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<meta name="keywords" content="R6RS Libraries (Guile Reference Manual)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Modules.html" rel="up" title="Modules">
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<link href="Variables.html" rel="next" title="Variables">
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<link href="R6RS-Version-References.html" rel="prev" title="R6RS Version References">
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<style type="text/css">
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</style>
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="R6RS-Libraries">
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<div class="nav-panel">
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<p>
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Next: <a href="Variables.html" accesskey="n" rel="next">Variables</a>, Previous: <a href="R6RS-Version-References.html" accesskey="p" rel="prev">R6RS Version References</a>, Up: <a href="Modules.html" accesskey="u" rel="up">Modules</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<h4 class="subsection" id="R6RS-Libraries-1"><span>6.18.6 R6RS Libraries<a class="copiable-link" href="#R6RS-Libraries-1"> ¶</a></span></h4>
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<p>In addition to the API described in the previous sections, you also
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have the option to create modules using the portable <code class="code">library</code> form
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described in R6RS (see <a data-manual="r6rs" href="../r6rs_html/Library-form.html#Library-form">R6RS Library Form</a> in <cite class="cite">The
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Revised^6 Report on the Algorithmic Language Scheme</cite>), and to import
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libraries created in this format by other programmers. Guile’s R6RS
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library implementation takes advantage of the flexibility built into the
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module system by expanding the R6RS library form into a corresponding
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Guile <code class="code">define-module</code> form that specifies equivalent import and
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export requirements and includes the same body expressions. The library
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expression:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> (library (mylib (1 2))
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(export mybinding)
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(import (otherlib (3))))
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</pre></div>
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<p>is equivalent to the module definition:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> (define-module (mylib)
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#:version (1 2)
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#:use-module ((otherlib) #:version (3))
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#:export (mybinding))
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</pre></div>
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<p>Central to the mechanics of R6RS libraries is the concept of import
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and export <em class="dfn">levels</em>, which control the visibility of bindings at
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various phases of a library’s lifecycle — macros necessary to
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expand forms in the library’s body need to be available at expand
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time; variables used in the body of a procedure exported by the
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library must be available at runtime. R6RS specifies the optional
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<code class="code">for</code> sub-form of an <em class="emph">import set</em> specification (see below)
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as a mechanism by which a library author can indicate that a
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particular library import should take place at a particular phase
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with respect to the lifecycle of the importing library.
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</p>
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<p>Guile’s library implementation uses a technique called
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<em class="dfn">implicit phasing</em> (first described by Abdulaziz Ghuloum and R.
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Kent Dybvig), which allows the expander and compiler to automatically
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determine the necessary visibility of a binding imported from another
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library. As such, the <code class="code">for</code> sub-form described below is ignored by
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Guile (but may be required by Schemes in which phasing is explicit).
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-library"><span class="category-def">Scheme Syntax: </span><span><strong class="def-name">library</strong> <var class="def-var-arguments">name (export export-spec ...) (import import-spec ...) body ...</var><a class="copiable-link" href="#index-library"> ¶</a></span></dt>
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<dd><p>Defines a new library with the specified name, exports, and imports,
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and evaluates the specified body expressions in this library’s
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environment.
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</p>
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<p>The library <var class="var">name</var> is a non-empty list of identifiers, optionally
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ending with a version specification of the form described above
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(see <a class="pxref" href="Creating-Guile-Modules.html">Creating Guile Modules</a>).
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</p>
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<p>Each <var class="var">export-spec</var> is the name of a variable defined or imported
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by the library, or must take the form
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<code class="code">(rename (internal-name external-name) ...)</code>, where the
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identifier <var class="var">internal-name</var> names a variable defined or imported
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by the library and <var class="var">external-name</var> is the name by which the
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variable is seen by importing libraries.
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</p>
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<p>Each <var class="var">import-spec</var> must be either an <em class="dfn">import set</em> (see below)
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or must be of the form <code class="code">(for import-set import-level ...)</code>,
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where each <var class="var">import-level</var> is one of:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> run
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expand
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(meta <var class="var">level</var>)
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</pre></div>
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<p>where <var class="var">level</var> is an integer. Note that since Guile does not
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require explicit phase specification, any <var class="var">import-set</var>s found
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inside of <code class="code">for</code> sub-forms will be “unwrapped” during
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expansion and processed as if they had been specified directly.
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</p>
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<p>Import sets in turn take one of the following forms:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> <var class="var">library-reference</var>
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(library <var class="var">library-reference</var>)
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(only <var class="var">import-set</var> <var class="var">identifier</var> ...)
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(except <var class="var">import-set</var> <var class="var">identifier</var> ...)
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(prefix <var class="var">import-set</var> <var class="var">identifier</var>)
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(rename <var class="var">import-set</var> (<var class="var">internal-identifier</var> <var class="var">external-identifier</var>) ...)
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</pre></div>
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<p>where <var class="var">library-reference</var> is a non-empty list of identifiers
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ending with an optional version reference (see <a class="pxref" href="R6RS-Version-References.html">R6RS Version References</a>), and the other sub-forms have the following semantics,
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defined recursively on nested <var class="var">import-set</var>s:
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</p>
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<ul class="itemize mark-bullet">
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<li>The <code class="code">library</code> sub-form is used to specify libraries for import
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whose names begin with the identifier “library.”
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</li><li>The <code class="code">only</code> sub-form imports only the specified <var class="var">identifier</var>s
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from the given <var class="var">import-set</var>.
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</li><li>The <code class="code">except</code> sub-form imports all of the bindings exported by
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<var class="var">import-set</var> except for those that appear in the specified list
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of <var class="var">identifier</var>s.
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</li><li>The <code class="code">prefix</code> sub-form imports all of the bindings exported
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by <var class="var">import-set</var>, first prefixing them with the specified
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<var class="var">identifier</var>.
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</li><li>The <code class="code">rename</code> sub-form imports all of the identifiers exported
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by <var class="var">import-set</var>. The binding for each <var class="var">internal-identifier</var>
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among these identifiers is made visible to the importing library as
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the corresponding <var class="var">external-identifier</var>; all other bindings are
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imported using the names provided by <var class="var">import-set</var>.
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</li></ul>
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<p>Note that because Guile translates R6RS libraries into module
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definitions, an import specification may be used to declare a
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dependency on a native Guile module — although doing so may make
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your libraries less portable to other Schemes.
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</p>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-import-1"><span class="category-def">Scheme Syntax: </span><span><strong class="def-name">import</strong> <var class="def-var-arguments">import-spec ...</var><a class="copiable-link" href="#index-import-1"> ¶</a></span></dt>
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<dd><p>Import into the current environment the libraries specified by the
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given import specifications, where each <var class="var">import-spec</var> takes the
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same form as in the <code class="code">library</code> form described above.
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</p></dd></dl>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Variables.html">Variables</a>, Previous: <a href="R6RS-Version-References.html">R6RS Version References</a>, Up: <a href="Modules.html">Modules</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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