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<title>Issue 3429: "models" should subsume like "satisfies"</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#New">New</a> status.</em></p>
<h3 id="3429"><a href="lwg-active.html#3429">3429</a>. "models" should subsume like "satisfies"</h3>
<p><b>Section:</b> 16.4.5.11 <a href="https://wg21.link/res.on.requirements">[res.on.requirements]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Tim Song <b>Opened:</b> 2020-04-07 <b>Last modified:</b> 2020-09-06</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#res.on.requirements">active issues</a> in [res.on.requirements].</p>
<p><b>View all other</b> <a href="lwg-index.html#res.on.requirements">issues</a> in [res.on.requirements].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
It has been pointed out both on the LWG reflector and as 
<a href="https://github.com/cplusplus/draft/issues/3912">editorial issue 3912</a> that the
definition of "models" added in <a href="https://wg21.link/p2101r0">P2101R0</a> 
is not a model of clarity when a concept is defined in terms of other concepts.
</p>

<p><i>[2020-04-25 Issue Prioritization]</i></p>

<p>Priority to 3 after reflector discussion. There was a temptation to resolve this as P0, but
concerns were expressed that the "satisfied as part of the satisfaction" part was a bit confusing.</p>


<p id="res-3429"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4861">N4861</a>.
</p>

<ol>
<li><p>Modify 16.4.5.11 <a href="https://wg21.link/res.on.requirements">[res.on.requirements]</a> as indicated:</p>

<blockquote>
<p>
-1- A sequence <code>Args</code> of template arguments is said to <em>model</em> a concept <code>C</code> 
if<ins>:</ins> 
<ol style="list-style-type: none">
<li><p>(1.1) &mdash; <code>Args</code> satisfies <code>C</code> (13.5.3 <a href="https://wg21.link/temp.constr.decl">[temp.constr.decl]</a>)<ins>;</ins></p></li>
<li><p>(1.2) &mdash; <del>and</del><ins><code>Args</code></ins> meets all semantic requirements (if any) 
given in the specification of <code>C</code><ins>; and</ins></p></li>
<li><p>(1.3) &mdash; <ins>every concept found to be satisfied as part of the satisfaction 
determination above is also modeled</ins>.</p></li>
</ol>
</p>
</blockquote>
</li>
</ol>




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