So, this webpage has a strange attractor of the form:
$$x_{n+1} = a x_n + y_n$$ $$y_{n+1} = b + (x_n)^2$$
...it precedes the graphic of a strange attractor itself (the initial conditions are also given for the strange attractor). My question is, how can we prove that this system defines a strange attractor? Also, is there any way to get more exact values for the system - for example, more accurate numbers?
EDIT
I asked this question for a general reference on chaos and strange attractors. For this question (the current question), I'm wondering what exactly we need to do to prove that we have a strange attractor. In other words, the last question was a reference request, and this question is the mathematics itself - how do we go about proving that we've found a strange attractor?