I am following the mathmatical definiton of isomorphism:
The two sets are Quadtree instances and calls of `myself`. The map from calls to instances is "instance that was given as argument". This map is obviously bijective. The structure that is preserved is "is a child of".
The two sets are Quadtree instances and calls of `myself`. The map from calls to instances is "instance that was given as argument". This map is obviously bijective. The structure that is preserved is "is a child of".
QED :)