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<!--Weave of 'Basic Nonterminals' generated by Inweb-->
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<ul class="crumbs"><li><a href="../index.html">Home</a></li><li><a href="../compiler.html">Shared Modules</a></li><li><a href="index.html">words</a></li><li><a href="index.html#4">Chapter 4: Parsing</a></li><li><b>Basic Nonterminals</b></li></ul></div>
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<p class="purpose">A handful of bare minimum Preform syntax.</p>
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<ul class="toc"><li><a href="4-bn.html#SP1">§1. Text positions</a></li><li><a href="4-bn.html#SP3">§3. Balancing</a></li><li><a href="4-bn.html#SP5">§5. Literal numbers</a></li><li><a href="4-bn.html#SP6">§6. Literal text</a></li></ul><hr class="tocbar">
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<p class="commentary firstcommentary"><a id="SP1"></a><b>§1. Text positions. </b>A useful nonterminal which matches no text, but detects the position:
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="reserved-syntax">if</span><span class="plain-syntax">-</span><span class="identifier-syntax">start</span><span class="plain-syntax">-</span><span class="identifier-syntax">of</span><span class="plain-syntax">-</span><span class="identifier-syntax">paragraph</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">0</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">w1</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><span class="identifier-syntax">w1</span><span class="plain-syntax"> == </span><span class="constant-syntax">0</span><span class="plain-syntax">) || (</span><span class="identifier-syntax">compare_word</span><span class="plain-syntax">(</span><span class="identifier-syntax">w1</span><span class="plain-syntax">-1, </span><span class="identifier-syntax">PARBREAK_V</span><span class="plain-syntax">))) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP2"></a><b>§2. </b>And another convenience:
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="reserved-syntax">if</span><span class="plain-syntax">-</span><span class="identifier-syntax">not</span><span class="plain-syntax">-</span><span class="identifier-syntax">deliberately</span><span class="plain-syntax">-</span><span class="identifier-syntax">capitalised</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">0</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">int</span><span class="plain-syntax"> </span><span class="identifier-syntax">w1</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">);</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><a href="4-nw.html#SP5" class="function-link"><span class="function-syntax">Word::unexpectedly_upper_case</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">w1</span><span class="plain-syntax">) == </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">) </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP3"></a><b>§3. Balancing. </b>The following matches any text in which braces and brackets are correctly
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paired.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="identifier-syntax">balanced</span><span class="plain-syntax">-</span><span class="identifier-syntax">text</span><span class="plain-syntax">> ::=</span>
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<span class="plain-syntax"> ......</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP4"></a><b>§4. </b>Inform contains relatively few syntaxes where commas are actually required,
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though they can optionally be used in many lists, as here:
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</p>
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<blockquote>
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<p>parma ham, camembert, grapes</p>
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</blockquote>
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<p class="commentary">But for when we only want to spot comma placements, this can be used. Note
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that the comma matches only if not in brackets.
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="identifier-syntax">list</span><span class="plain-syntax">-</span><span class="identifier-syntax">comma</span><span class="plain-syntax">-</span><span class="identifier-syntax">division</span><span class="plain-syntax">> ::=</span>
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<span class="plain-syntax"> ...... , ......</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP5"></a><b>§5. Literal numbers. </b>(Inform itself doesn't use this, but has alternatives for cardinals and
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ordinals within the VM-representable range.)
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="identifier-syntax">any</span><span class="plain-syntax">-</span><span class="identifier-syntax">integer</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> (</span><a href="2-vcb.html#SP11" class="function-link"><span class="function-syntax">Vocabulary::test_flags</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">), </span><span class="constant-syntax">NUMBER_MC</span><span class="plain-syntax">)) {</span>
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<span class="plain-syntax"> *</span><span class="identifier-syntax">X</span><span class="plain-syntax"> = </span><a href="2-vcb.html#SP9" class="function-link"><span class="function-syntax">Vocabulary::get_literal_number_value</span></a><span class="plain-syntax">(</span><a href="3-lxr.html#SP18" class="function-link"><span class="function-syntax">Lexer::word</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)));</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP6"></a><b>§6. Literal text. </b>Text is "with substitutions" if it contains square brackets, used in Inform
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for interpolations called "text substitutions".
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="identifier-syntax">quoted</span><span class="plain-syntax">-</span><span class="identifier-syntax">text</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><a href="3-wrd.html#SP12" class="function-link"><span class="function-syntax">Wordings::nonempty</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)) && (</span><a href="2-vcb.html#SP11" class="function-link"><span class="function-syntax">Vocabulary::test_flags</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">), </span><span class="constant-syntax">TEXT_MC</span><span class="plain-syntax">+</span><span class="constant-syntax">TEXTWITHSUBS_MC</span><span class="plain-syntax">))) {</span>
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<span class="plain-syntax"> *</span><span class="identifier-syntax">X</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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<span class="plain-syntax"><</span><span class="identifier-syntax">quoted</span><span class="plain-syntax">-</span><span class="identifier-syntax">text</span><span class="plain-syntax">-</span><span class="identifier-syntax">with</span><span class="plain-syntax">-</span><span class="identifier-syntax">subs</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><a href="3-wrd.html#SP12" class="function-link"><span class="function-syntax">Wordings::nonempty</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)) && (</span><a href="2-vcb.html#SP11" class="function-link"><span class="function-syntax">Vocabulary::test_flags</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">), </span><span class="constant-syntax">TEXTWITHSUBS_MC</span><span class="plain-syntax">))) {</span>
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<span class="plain-syntax"> *</span><span class="identifier-syntax">X</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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<span class="plain-syntax"><</span><span class="identifier-syntax">quoted</span><span class="plain-syntax">-</span><span class="identifier-syntax">text</span><span class="plain-syntax">-</span><span class="identifier-syntax">without</span><span class="plain-syntax">-</span><span class="identifier-syntax">subs</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><a href="3-wrd.html#SP12" class="function-link"><span class="function-syntax">Wordings::nonempty</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)) && (</span><a href="2-vcb.html#SP11" class="function-link"><span class="function-syntax">Vocabulary::test_flags</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">), </span><span class="constant-syntax">TEXT_MC</span><span class="plain-syntax">))) {</span>
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<span class="plain-syntax"> *</span><span class="identifier-syntax">X</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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</pre>
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<p class="commentary firstcommentary"><a id="SP7"></a><b>§7. </b>For finicky technical reasons the easiest way to detect an empty piece
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of text <span class="extract"><span class="extract-syntax">""</span></span> is to provide a nonterminal matching it:
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</p>
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<pre class="displayed-code all-displayed-code code-font">
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<span class="plain-syntax"><</span><span class="identifier-syntax">empty</span><span class="plain-syntax">-</span><span class="identifier-syntax">text</span><span class="plain-syntax">> </span><span class="identifier-syntax">internal</span><span class="plain-syntax"> </span><span class="constant-syntax">1</span><span class="plain-syntax"> {</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">if</span><span class="plain-syntax"> ((</span><a href="3-wrd.html#SP12" class="function-link"><span class="function-syntax">Wordings::nonempty</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">)) && (</span><a href="4-nw.html#SP2" class="function-link"><span class="function-syntax">Word::compare_by_strcmp</span></a><span class="plain-syntax">(</span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">), </span><span class="identifier-syntax">L</span><span class="string-syntax">"\"\""</span><span class="plain-syntax">))) {</span>
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<span class="plain-syntax"> *</span><span class="identifier-syntax">X</span><span class="plain-syntax"> = </span><a href="3-wrd.html#SP8" class="function-link"><span class="function-syntax">Wordings::first_wn</span></a><span class="plain-syntax">(</span><span class="identifier-syntax">W</span><span class="plain-syntax">); </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">TRUE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax"> }</span>
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<span class="plain-syntax"> </span><span class="reserved-syntax">return</span><span class="plain-syntax"> </span><span class="identifier-syntax">FALSE</span><span class="plain-syntax">;</span>
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<span class="plain-syntax">}</span>
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</pre>
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