Kleene fixed-point theorem

Etymology
Named after American mathematician Stephen Cole Kleene.

Proper noun

 * 1)  Suppose $$(L, \sqsubseteq)$$ is a directed-complete partial order with a least element, and let $$f: L \to L$$ be a Scott-continuous (and therefore monotone) function. Then $$f$$ has a least fixed point, which is the supremum of the ascending Kleene chain of $$f$$.