I have a doubt in which I hope someone could help me. I would like to write a book about how to use UDK, teaching the basics, I read that I can do that as an unofficial documentation but the content should be new and original and not republish content from official publishing such as the Mastering Unreal Technology books. On my book, of course I plan to write everything based on my own experience, but I would cover topics that I imagine come inside official documentation such as user interface, material editor and some other basic stuff. My question is: Can I write a book about how to use UDK even that I cover topics that may be already included in official documentation but based on my own experience and in my own words? and if I can, do I need a license to do it?