'Chaos esthétique' in a dynamical system of Igor Gumowski and Christian Mira (1973). Originally this system was used as a model of the longitudinal motion of nuclear particles in an accelerator at CERN.

The following general map is used:
x' = y + F(x), y' = -x + F(x'),
in which:
F(x) = ax + 2(1 – a)x² / (1 + x²)

From the book of Hans Lauwerier, Spelen met Graphics en Fractals, Academic Service 1994, (with programs in BASIC).
Also see: http://mariefrance.hellot.free.fr/Mira.html and https://www.researchgate.net/publication/263469351

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