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<html>
<head><title>HIDDEN-DEATH-PACKAGE.html -- ACL2 Version 3.1</title></head>
<body text=#000000 bgcolor="#FFFFFF">
<h3>HIDDEN-DEATH-PACKAGE</h3>handling <code><a href="DEFPKG.html">defpkg</a></code> <a href="EVENTS.html">events</a> that are <code><a href="LOCAL.html">local</a></code>
<pre>Major Section: <a href="DEFPKG.html">DEFPKG</a>
</pre><p>
This documentation topic explains a little bit about certain errors users may
see when attempting to evaluate a <code><a href="DEFPKG.html">defpkg</a></code> event. In brief, if you see
an error that refers you to this topic, you are probably trying to admit a
<code><a href="DEFPKG.html">defpkg</a></code> event, and you should change the name of the package to be
introduced by that event.<p>
Recall that <code>defpkg</code> events introduce axioms, for example as follows.
<pre>
ACL2 !>(defpkg "PKG0" '(a b))<p>
Summary
Form: ( DEFPKG "PKG0" ...)
Rules: NIL
Warnings: None
Time: 0.01 seconds (prove: 0.00, print: 0.00, other: 0.01)
"PKG0"
ACL2 !>:pr! "PKG0"<p>
Rune: (:REWRITE PKG0-PACKAGE)
Status: Enabled
Lhs: (SYMBOL-PACKAGE-NAME (INTERN-IN-PACKAGE-OF-SYMBOL X Y))
Rhs: "PKG0"
Hyps: (AND (STRINGP X)
(NOT (MEMBER-SYMBOL-NAME X '(A B)))
(SYMBOLP Y)
(EQUAL (SYMBOL-PACKAGE-NAME Y) "PKG0"))
Equiv: EQUAL
Backchain-limit-lst: NIL
Subclass: BACKCHAIN
Loop-stopper: NIL
ACL2 !>
</pre>
Now, a <code><a href="DEFPKG.html">defpkg</a></code> event may be executed underneath an <code><a href="ENCAPSULATE.html">encapsulate</a></code> or
<code><a href="INCLUDE-BOOK.html">include-book</a></code> form that is marked <code><a href="LOCAL.html">local</a></code>. In that case, traces of
the added axiom will disappear after the surrounding <code><a href="ENCAPSULATE.html">encapsulate</a></code> or
<code><a href="INCLUDE-BOOK.html">include-book</a></code> form is admitted. This can cause inconsistencies. (You
can take our word for it, or you can look at the example shown in the
``Essay on Hidden Packages'' in source file <code>axioms.lisp</code>.)<p>
In order to prevent unsoundness, then, ACL2 maintains the following
invariant. Let us say that a <code>defpkg</code> event is ``hidden'' if it is in
support of the current logical <a href="WORLD.html">world</a> but is not present in that world as
an event, because it is <code><a href="LOCAL.html">local</a></code> as indicated above. We maintain the
invariant that all <code><a href="DEFPKG.html">defpkg</a></code> <a href="EVENTS.html">events</a>, even if ``hidden'', are tracked
under-the-hood in the current logical <a href="WORLD.html">world</a>. Sometimes this property
causes <code><a href="DEFPKG.html">defpkg</a></code> events to be written to the <a href="PORTCULLIS.html">portcullis</a> of a book's
<a href="CERTIFICATE.html">certificate</a> (see <a href="BOOKS.html">books</a>). At any rate, if you then try to define the
package in a manner inconsistent with the earlier such definition, that is,
with a different imports list, you will see an error because of the
above-mentioned tracking.<p>
(By the way, this topic's name comes from Holly Bell, who heard
"hidden death package" instead of "hidden defpkg". The description
seemed to fit. Thanks, Holly!)
<p>
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