Part I. 1. Introduction.- 2. What is Structure?.- 3. Category Theory.- 4. How to Trick the Demon of Entropy.- 5. Neural Networks and Groupoids.- Part II. 6. Natural Intelligence in the Wild.- 7. Natural Intelligence is about meaning.- 8. From Identity to Equivalence.- 9. On Negation.- 10. Modeling.- 11. On Structures and Wholes.- Part III. 12. Let's Talk About Nothing.- 13. King Richard is a Lion....