Global logical variables

<BODY bgcolor="#ffeee0" text="#000000" link="#9944EE" vlink="#FF0000" alink="#00ff00">  <A HREF="node20_mn.html" TARGET="_top"> <IMG WIDTH="37" HEIGHT="24" ALT="next" SRC="next.png"></A> <A HREF="node18_mn.html" TARGET="_top"> <IMG WIDTH="26" HEIGHT="24" ALT="up" SRC="up.png"></A> <A HREF="node18_mn.html" TARGET="_top"> <IMG WIDTH="63" HEIGHT="24" ALT="previous" SRC="prev.png"></A> <BR> <B> Next:</B> <A HREF="node20_mn.html" TARGET="_top">Garbage-collectible permanent objects.</A> <B> Up:</B> <A HREF="node18_mn.html" TARGET="_top">The Blackboard</A> <B> Previous:</B> <A HREF="node18_mn.html" TARGET="_top">The Blackboard</A> <BR> <BR> <P> Sorry, this requires a browser that supports frames! <BR> Try <A HREF="node19_ct.html">node19_ct.html</A> instead.</P> <HR>