Function Composition
Feed one function's output into another.
Concept
Work from the inside out
(f ∘ g)(x) means f(g(x)): evaluate g first, then hand the result to f.
Order matters. f(g(x)) and g(f(x)) are usually different functions, so read the parentheses carefully.
(f ∘ g)(x) = f(g(x))