Some example source files depend on PYTHIA 6 and HERWIG 6, which have no
license so cannot be distributed within Debian.

I created Debian packaging stuff of these packages, however. To build and
install them, run the commands below (you need install the "git" package first)
and follow the instructions in pythia6/INSTALL and herwig6/INSTALL:

$ git clone git://git.debian.org/git/debian-science/packages/pythia6.git
$ git clone git://git.debian.org/git/debian-science/packages/herwig6.git

