The mathematics of mathematics — made visual through 41 interactive demonstrations.
The atoms of category theory: objects, arrows, and hom-sets
How arrows compose, identity morphisms, and associativity
Set, Grp, Top, Vect, and poset categories in action
Structure-preserving maps between categories
Morphisms between functors and the naturality square
Universal properties, Cartesian products, and disjoint unions
Cones, pullbacks, equalizers, and the limit zoo
The most important concept: free-forgetful pairs and hom-set bijections
You are what you relate to: representable functors and presheaves
Monads from adjunctions and the string diagram calculus