Complex Systems
Complex systems are systems where the collective behavior of their parts entails emergence of properties that can hardly, if not at all, be inferred from properties of the parts.
Jason Badeaux and
Complex Systems
Fermat's Library | Life's Irreducible Structure annotated/explained version.
fermatslibrary.com
(Annotated).
The Theory of Constraints is a good example of how we are surrounded by complicated systems where the optimal strategy, by definition, is always a simple one: in this case, attack the biggest constraint.