https://sites.google.com/site/mycoopera/ ::::: https://web.archive.org/web/20091115161911/http://www.polygraphicum.de/refs.html

https://sites.google.com/site/mycoopera/ https://sites.google.com/view/he1m/home

https://sites.google.com/site/mycoopera/ https://sites.google.com/view/he1m/home https://web.archive.org/web/20091115161911/http://www.polygraphicum.de/refs.html