Take a paper ribbon of any width and make a knot in it. Go gently. Make the knot as flat and neat as you can. It will be pentagonal. With some practice, the pentagon will be perfect. If you look through it toward a light source, you will see embedded in it a pentagonal star minus one of its five edges. Now, I have been making such knots for years. I have been marveling at them all the while. Chances are many others have noticed this geometric peculiarity of ribbons, but I have not yet stumbled upon it in the public domain. At long last, I feel compelled to leave a small trace of the pentagonal ribbon knot in my Residua.