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The <code>IFZERO</code> macro expects three parameter lists, just as the other
<code>IF...</code> macros: a symbol, a true-list and a false-list. 

The first argument defines whether the whole macro expands to the true-list or
to the false-list. The first argument may be:

<dl>

<li > Nothing (empty): the macro expands to the true-list.

<li > A number: when zero, the macro expands to the true-list.

<li > The name of a counter: when the value of the counter is zero, the
    macro expands to the true-list. 

<li > Anything else: the macro expands to the false-list.

</dl>

You can use <code>COUNTERVALUE(somecounter)</code> as the argument to <code>IFZERO</code>, it is
treated in the same manner as the corresponding counter name. 

Example: The <code>IFZERO</code> macro offers a very simple way to pass a flag-argument
(an on/off switch) to a macro. E.g., in LaTeX you start environments with
<code>\begin{environment}</code> and end them with <code>\end{environment}</code>;
<code>environment</code> being e.g., <code>center</code>, <code>flushright</code>, <code>flushleft</code>. A
possible meta-macro for the environments might be:

<pre>
DEFINEMACRO(environment)(2)(\ 
    IFZERO(ARG2)\ 
        NOEXPAND(\end{ARG1})\ 
        NOEXPAND(\begin{ARG1}))
</pre>

<p>Such a macro may be used as:
<p><pre>
environment(center)(1)
Now comes centered text.
environment(center)(0)
</pre>

<p>which would of course lead to <code>\begin</code> and <code>\end{center}</code>. The numeric
second argument is used here as a on/off switch.
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Copyright (c) 1997, 1998, 1999 Karel Kubat and Jan Nieuwenhuizen.

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