\doc{The define-class command}
\ref{define-class-command}

The \def{define-class command} introduces an abbreviation for a set of named
facts.  This abbreviation can be used wherever \s{names} are required as an
argument to a command.

\head{2}{\dlink{../symbols/syntax}{Syntax}}
\begin{verbatim}
\sd{define-class-command} ::= \f{define-class} \slink{../misc/class}{class-name} [ \slink{../misc/names}{names} ]
\end{verbatim}

\head{2}{Examples}
\begin{verbatim}
define-class $facts nat, set
define-class $facts1 copy($facts)
define-class $old eval(*)
\end{verbatim}

\head{2}{Usage} 
The \fq{define-class} command defines \s{class-name} as an abbreviation for
\s{names}.  If no \s{names} are specified, the command prints the current
definition of \s{class-name}.  The examples define the following abbreviations:
\begin{itemize}
\item 
\f{$facts} is an abbreviation for \fq{nat, set}.  The command 
\fq{display $facts} is equivalent to the command \fq{display nat, set}.
\p
\item
\f{$facts1} is also an abbreviation for \fq{nat, set}.  Without the \fq{copy}
operation, it would be an abbreviation for \f{$facts}, whose meaning would
change if \f{$facts} was redefined.
\p
\item
\f{$old} is an abbreviation for the list of names of all facts in LP's logical 
system when the \fq{define-class} command was executed; the \fq{eval} operation
forces the evaluation of its argument \fq{*}.  The command
\fq{display $old} displays the current forms of any of those facts that are
still in LP's logical system when the \fq{display} command is executed.
\end{itemize}

See also \slink{../miscs/name}{name}.