Composition

#Catagory
There are two extremely important properties that the composition in any category must satisfy.

1. Composition is associative

f :: A -> B 
g :: B -> C 
h :: C -> D 
h . (g . f) == (h . g) . f == h . g . f

2. For every object $A$ there is an arrow which is a unit of composition. This arrow loops from the object to itself.

let id x = x