We study the class of operations definable from the given operations of an algebra of sets by union, composition, and fixed points; we obtain two theorems on definable operations that give us as special case the regular-equsls-recognisable theorem of generalised ~inite automata theory.Definable operations arise also as the operations computable by chartsj by translating into predicate logic, we obtain Manna's formulas ~or termination and correctness of flowcharts.~o be published in Machine Intelli~ence 5, Edinbur~
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