timelets

their [the categorical concepts'] simplicity was accessible only through graduate-level textbooks, because the available examples involved topics such as modules and topological spaces.

Our solution to that dilemma was to develop from the basics the concepts of directed graph and of discrete dynamical system, which are mathematical structures of wide importance that are nevertheless accessible to any interested high-school student.

--- Lawvere & Schanuel, 2009.

It's an amazing feat to simplify fundamentally simple concepts without dumbing them down.