Moved author and date to boilerplate.tex.
Added copyright.tex to all files.
Added descr of check_interval to libsys.tex.
Corrected lotsa typos in tut.tex (thanks to George M. Sipe).
Corrected mktuple (should be newtupleobject) example in ext.tex.
diff --git a/Doc/copyright.tex b/Doc/copyright.tex
new file mode 100644
index 0000000..f445c40
--- /dev/null
+++ b/Doc/copyright.tex
@@ -0,0 +1,22 @@
+Copyright 1991, 1992, 1993, 1994 by Stichting Mathematisch Centrum,
+Amsterdam, The Netherlands.
+
+\begin{center}
+All Rights Reserved
+\end{center}
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose and without fee is hereby granted,
+provided that the above copyright notice appear in all copies and that
+both that copyright notice and this permission notice appear in
+supporting documentation, and that the names of Stichting Mathematisch
+Centrum or CWI not be used in advertising or publicity pertaining to
+distribution of the software without specific, written prior permission.
+
+STICHTING MATHEMATISCH CENTRUM DISCLAIMS ALL WARRANTIES WITH REGARD TO
+THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+FITNESS, IN NO EVENT SHALL STICHTING MATHEMATISCH CENTRUM BE LIABLE
+FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
+OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.