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<head><title>GUARD-QUICK-REFERENCE.html -- ACL2 Version 3.1</title></head>
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<h3>GUARD-QUICK-REFERENCE</h3>brief summary of guard checking and guard verification
<pre>Major Section: <a href="GUARD.html">GUARD</a>
</pre><p>
For a careful introduction to guards, see <a href="GUARD.html">guard</a>.
<p>
<b>I. GUARD CHECKING DURING EXECUTION</B><p>
<em>Effect</em><p>
Guards on definitions are checked at execution time (except for
guards on subsidiary calls of recursive or mutually recursive
functions).<p>
<em>When does it happen</em><p>
By default, guards are checked for all forms submitted at the top
level.<p>
<em>To disable</em><br>
<code>:set-guard-checking nil</code> ; skip raw Lisp if there is a guard violation
<code>:set-guard-checking :none</code> ; skip guard checking entirely<p>
<em>To (re-)enable</em><br>
<code>:set-guard-checking t</code><p>
See <a href="SET-GUARD-CHECKING.html">set-guard-checking</a> for more options.<p>
<b>II. GUARD VERIFICATION</B><p>
<em>Effect</em><p>
A proof is attempted of the obligations arising from the guards of
subsidiary functions in a <code><a href="DEFUN.html">defun</a></code>, <code><a href="DEFTHM.html">defthm</a></code>, or <code><a href="DEFAXIOM.html">defaxiom</a></code> event.
In the case of a <code>defun</code>, the guard itself is also verified (under an
implicit guard of <code>t</code>).<p>
<em>When does it happen</em><p>
Only names of defined functions, <code><a href="DEFTHM.html">defthm</a></code>s, and <code><a href="DEFAXIOM.html">defaxiom</a></code>s are
subject to guard verification. Guard verification may occur when
functions are defined (using <code><a href="DEFUN.html">defun</a></code>), but it requires an explicit
call of <code><a href="VERIFY-GUARDS.html">verify-guards</a></code> in order to verify guards for <code><a href="DEFTHM.html">defthm</a></code>s
and <code><a href="DEFAXIOM.html">defaxiom</a></code>s. Constrained functions (see <a href="ENCAPSULATE.html">encapsulate</a>) may
not have their guards verified.<p>
<code>(verify-guards foo ...)</code><br>
causes guard verification for the <code><a href="DEFUN.html">defun</a></code>, <code><a href="DEFTHM.html">defthm</a></code>, or <code><a href="DEFAXIOM.html">defaxiom</a></code> named
by <code>foo</code>, if it has not already been successfully done. The default
<a href="DEFUN-MODE.html">defun-mode</a> (see <a href="DEFAULT-DEFUN-MODE.html">default-defun-mode</a>) must be <code>:</code><code><a href="LOGIC.html">logic</a></code>, or else
this event is ignored.<p>
<code>(defun foo ...)</code><br>
causes guard verification of <code>foo</code> if and only if the following
conditions are both met. (However,
see <a href="SET-VERIFY-GUARDS-EAGERNESS.html">set-verify-guards-eagerness</a> for how to change this
behavior.)
<blockquote>
1. Foo is processed in <code>:</code><code><a href="LOGIC.html">logic</a></code> mode (either by setting mode <code>:</code><code><a href="LOGIC.html">logic</a></code>
globally, or by including <code>:mode :logic</code> in the <code><a href="XARGS.html">xargs</a></code> declaration).<p>
2. The <code><a href="XARGS.html">xargs</a></code> declaration (see <a href="XARGS.html">xargs</a>) either specifies <code>:</code><code><a href="GUARD.html">guard</a></code> or
specifies <code>:</code><code><a href="VERIFY-GUARDS.html">verify-guards</a></code> <code>t</code> (or both).
</blockquote>
<p>
<code>(verify-termination foo ...)</code><br>
causes guard verification of <code>foo</code> if <code>foo</code> is a function currently
defined in <code>:</code><code><a href="PROGRAM.html">program</a></code> mode and the appropriate <code><a href="XARGS.html">xargs</a></code> are supplied, as
discussed for the case of <code><a href="DEFUN.html">defun</a></code> above. The default <a href="DEFUN-MODE.html">defun-mode</a>
(see <a href="DEFAULT-DEFUN-MODE.html">default-defun-mode</a>) must be <code>:</code><code><a href="LOGIC.html">logic</a></code>, or else this event is
ignored.
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