involution operation

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involution operation Any monadic operation f that satisfies the law f(f(a)) = a

for all a in the domain of f. The law is known as the involution law. It is satisifed by the elements of a Boolean algebra where the monadic function is the process of taking a complement. Taking complements of sets and negation in its different forms also satisfy the law, as does the principle of duality as it applies in Boolean algebras.