COS2Z Blind Spot Lockets

Newton's method applied to f(z) = z^7 - z^3 + cos(2z), framed on the whole mirror-symmetric plate from Re z in [-10, 10] and Im z in [-14, 14]. Doubling the cosine frequency makes the band where |cos 2z| matches |z^7| repeat every pi in Re z, so a seven-arm burst at the origin sits inside an arcade of dark arches. Colour is driven by the step count from wine through copper to white, with a small per-basin shift in warmth.