Kleene fixed-point theorem

The Kleene fixed-point theorem is a fundamental result in theoretical computer science and mathematical logic, particularly in the context of domain theory and functional programming. Named after Stephen Cole Kleene, it provides a framework for understanding the existence of fixed points in certain types of functions. In simple terms, a fixed point of a function \( f \) is a value \( x \) such that \( f(x) = x \).