 Theorem 2.1 (The Fixed Point Theorem for continuous functions) Let \(f : D \to D\) be a continuous function and \(x \in D\) be such that \(x \sqsubseteq f(x)\). Then the element   \[\bigsqcup_{n \in {\mathbb{N}}} f^{(n)}(x)\]  is the least \(y \sqsupseteq x\) such that \(f(y) = y\).