I was afraid that it is too trivial to write about, because once you get the idea it seems so common sense. After all, (a+b)(a+b) = aa + 2ab + bb, so you can observe the inner square right in the algebra. But, I never paid attention to it. So, I’m glad that I’m not the only one who found the scheme brilliant. Algebra takes a whole new meaning, when you can link it back to geometry.