Isoptics of a parabola
Related papers:
N. Zehavi, G. Mann and Th. Dana-Picard, (in Hebrew) (2007): What can
be learnt when changing the point of view on conic sections?, Aleh 38, 22-31.
Th. Dana-Picard, G. Mann and N. Zehavi (2011): From conic intersectionsto toric intersections: the case of the isoptic curves of an ellipse, The Montana Mathematical Enthusiast 9 (1), 59-76.