Iteration is a fundamental concept in googology in which a function is composed with itself repeatedly.[1] Given a function $$f \colon X \to Y$$ with $$X \supseteq Y$$, we use $$f^n(x)$$ to refer to the result when applying $$f$$ to $$x$$ $$n$$ times. Formally, $$f^0(x) = x$$ and $$f^{n + 1}(x) = f(f^{n}(x))$$.