In Figure 8 the legend includes: "Clockwise from top left:period 3 bulb, period 4 bulb, period 5 bulb. period 7 bulb." To agree with this, the two lower pictures should be swapped, I think. Anyway, that's just a minor point. I did not know about this relationship. Is the cause of it as simple as the generating function or as complex as the object?? I'm enjoying exploring the Mandelbrot set as I am learning Python. I've been interested in it since I read about it in A. K. Dewdney's article in Aug 1985 Scientific American, a copy of which is beside me as I write. Thank you.