Category Theory

In essence, a simple collection which can be thought of as a graph. Three components

1. A collection of objects (nodes)
2. A collection of morphisms (edges).
   • If $f$ is a morphism with source C and target B, we write $f:C\to B$
3. A notion of composition of morphisms.
   • If we have $g:A\to B$ and $f:B\to C$, they can be composed resulting in a morphism $f\circ g:A\to C$
   • Composition of morphisms needs to be associative. Typically applied right to left

See also: functional programming, Homotopy Theory