
So I was experimenting with fractals and created this. The equations are
$$ A \leftarrow A^2 + x - B \\ B \leftarrow B^2 - y + A $$ and the set is defined as the points (x,y) on a graph which when the equations are iterated, $A$ AND $B$ remain bounded.
(The colours in the graph are from the number of iterations required to surpass the threshold of $-2$ for either $A$ or $B$.)
Initial values for $A$ and $B$ are 0
if you are wandering about computation, it is iterated 216 times and the threshold for being considered not bound is $A$ or $B$ being over 10,000,000,000.
Not an answer but too long for a comment.
I reproduced the image with this code for shader editor app from fdroid for Android:
The grid spacing is 1, centered on the origin. Note the signs in the formula: $$ A_{n+1} = A_n^2 + x - B_n \\ B_{n+1} = B_n^2 + y + A_n $$