Could anybody please explain the concept of extended plane and extended space? I know the definition of an ideal point and that's the only part that I really understand. If each two distinct planes (in extended space) meet in just one line, does it mean that there's only one ideal line for each plane? What's the difference between extended plane and extended space? There's only one extended plane in extended space, right? I know that for some of you these questions will sound very silly, but the book I have has a very poor explanation. If you know some web page where I can learn the basics, please tell me. Thank you!