This is the Debian GNU/Linux prepackaged version of the perl module
Date::Calc renamed to libdate-calc-perl.

ftp://ftp.cpan.org/pub/CPAN/modules/by-module/Date/Date-Calc-4.2.tar.gz

This package with all its parts is

Copyright (c) 1995 - 2001 by Steffen Beyer.
All rights reserved.

This package is free software; you can use, modify and redistribute
it under the same terms as Perl itself, i.e., under the terms of
the "Artistic License" or the "GNU General Public License".

The C library at the core of this Perl module can additionally
be used, modified and redistributed under the terms of the
"GNU Library General Public License".

Please refer to the files "Artistic.txt", "GNU_GPL.txt" and
"GNU_LGPL.txt" in this distribution, respectively, for details!
You can find them in /usr/share/common-licenses/.