1. A question: by way of foreword2. Types and typologies3. A source of confidence4. Back to the origins5. A new formulation of an old concept6. Four in one7. The four temperaments in colour8. Born four times9. Up to the age of fourteen10. After twice seven years11. The number of the earth12. The four Evangelists13. The black square14. Fairy tales as a guide15. Moving mountains16. Seeing the wood through the trees17. Eating what's on the table18. Four children in the class19. In conclusion: an answer