``Fixed point'' finder
The ``Next Approximation'' circuit takes an approximate answer and produces a better one. Here, its output is connected to its input through delay-canceling negative time delays. If the whole circuit doesn't break, it is forced by a causal loop to snatch, instantly, out of thin air, a perfect solution that cannot be further refined.
Examine the figure in 3D.
(this needs a VRML plugin for your browser)