Kuratowski's Closure-Component Problem

Let $X$ be an arbitrary Topological Space. Denote the Closure of a Subset $A$ of $X$ by $A^-$ and the complement of $A$ by $A'$. Then at most 14 different Sets can be derived from $A$ by repeated application of closure and complementation (Berman and Jordan 1975, Fife 1991). The problem was first proved by Kuratowski (1922) and popularized by Kelley (1955).

See also Kuratowski Reduction Theorem

References

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Baron, S. Advanced Problem 5569. Amer. Math. Monthly 75, 199, 1968.

Berman, J. and Jordan, S. L. ``The Kuratowski Closure-Complement Problem.'' Amer. Math. Monthly 82, 841-842, 1975.

Buchman, E. ``Problem E 3144.'' Amer. Math. Monthly 93, 299, 1986.

Chagrov, A. V. ``Kuratowski Numbers, Application of Functional Analysis in Approximation Theory.'' Kalinin: Kalinin Gos. Univ., pp. 186-190, 1982.

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Kelley, J. L. General Topology. Princeton: Van Nostrand, p. 57, 1955.

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Levine, N. ``On the Commutativity of the Closure and Interior Operators in Topological Spaces.'' Amer. Math. Monthly 68, 474-477, 1961.

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Peleg, D. ``A Generalized Closure and Complement Phenomenon.'' Discrete Math. 50, 285-293, 1984.

Shum, K. P. ``On the Boundary of Kuratowski 14-Sets in Connected Spaces.'' Glas. Mat. Ser. III 19, 293-296, 1984.

Shum, K. P. ``The Amalgamation of Closure and Boundary Functions on Semigroups and Partially Ordered Sets.'' In Proceedings of the Conference on Ordered Structures and Algebra of Computer Languages. Singapore: World Scientific, pp. 232-243, 1993.

Smith, A. Advanced Problem 5996. Amer. Math. Monthly 81, 1034, 1974.

Soltan, V. P. ``On Kuratowski's Problem.'' Bull. Acad. Polon. Sci. Ser. Sci. Math. 28, 369-375, 1981.

Soltan, V. P. ``Problems of Kuratowski Type.'' Mat. Issled. 65, 121-131 and 155, 1982.