Abstraction for calculating the Hénon attractor

The "Hénon attractor" (or "Hénon map") is an iterative function that produces a particular chaotic pattern of behavior, which can be visualized or sonified. An iterative function is a formula that uses its own output as an input variable in its own subsequent calculation. In the case of the Hénon map, the function outputs two values, x and y, which can be considered as the coordinates of a point in two-dimensional Cartesian space.