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2017 Berghammer ARudolf Berghammer, Tool-Based Relational Investigation of Closure-Interior Relatives for Finite Topological Spaces, Relational and Algebraic Methods in Computer Science, Lecture Notes in Computer Science, v. 10226, edited by P. Höfner, D. Pous, G. Struth, 2017, pp. 60‑76.
2016 JJ AJozef Jirásek, Juraj Šebej, Kuratowski Algebras Generated by Prefix‑Free Languages, Implementation and Application of Automata, CIAA 2016, Lecture Notes in Computer Science, v. 9705, edited by Yo‑Sub Han, Kai Salomaa, pp. 150‑162.
2016 Schwiebert ARyan C. Schwiebert, The Radical-Annihilator Monoid of a Ring, Comm. Algebra, 2016.
2015 BCMPRS AT. Banakh, O. Chervak, T. Martynyuk, M. Pylypovych, A. Ravsky, M. Simkiv, Kuratowski Monoids of n‑Topological Spaces, arXiv:1508.07703 [math.GN],, 2015, 20 pp.
2014 SG ARatna Dev Sarma, Ankit Gupta, On the k‑Numbers of Some Generalized Kuratowski Operators in Topology, APMSCSET‑2014, pp. 50‑54.
2013 PW ASzymon Plewik, Marta Walczyńska, The Monoid Consisting of Kuratowski Operations, J. Math., v. 2013, 2013, pp. 1‑9.
2012 AMSS‑a AOsama Al-Hassani, Quratul‑ain Mahesar, Claudio Sacerdoti Coen, Volker Sorge, A Term Rewriting System for Kuratowski’s Closure-Complement Problem, Proceedings of the 23rd International Conference on Rewriting Techniques and Applications, RTA 2012, Nagoya, Japan, Monday, May 28, 2012 to Saturday, June 2, 2012, Leibniz International Proceedings in Informatics (LIPIcs), v. 15, edited by Ashish Tiwari, pp. 38‑52.
2012 AMSS‑b AOsama Al-Hassani, Quratul‑ain Mahesar, Claudio Sacerdoti Coen, Volker Sorge, Solving Kuratowski Problems by Term Rewriting, Proceedings of the 19th Automated Reasoning Workshop, 2‑4 April 2012, Manchester UK, edited by Fabio Papacchini, Renate A. Schmidt, pp. 51‑52.
2012 CDHS AÉmilie Charlier, Mike Domaratzki, Tero Harju, Jeffrey Shallit, Composition and Orbits of Language Operations: Finiteness and Upper Bounds, Intl. J. Comp. Math., 2012, pp. 1‑26.
2012 Cato ASusumu Cato, Complements and Consistent Closures, Discrete Math., v. 312, 2012, pp. 1218‑1221.
2012 PW ASzymon Plewik, Marta Walczyńska, Kuratowski Operations Revisited, arXiv:1205.3391 [math.GN],, 2012, 18 pp.
2011 BGS AJanusz Brzozowski, Elyot Grant, Jeffrey Shallit, Closures in Formal Languages and Kuratowski’s Theorem, Intl. J. Found. Comp. Sci., v. 22, 2011, pp. 301‑321.
2011 CDHS AÉmilie Charlier, Mike Domaratzki, Tero Harju, Jeffrey Shallit, Finite Orbits of Language Operations, Language and Automata Theory and Applications, Proceedings of the 5th International Conference, LATA 2011, Tarragona, Spain, May 26‑31, 2011, Lecture Notes in Computer Science, v. 6638, edited by A. H. Dediu, S. Inenaga, C. Martín-Vide, pp. 204‑215.
2011 HK AŠtěpán Holub, Juha Kortelainen, On Partitions Separating Words, Intl. J. Algebra Comp., v. 21 no. 8, 2011, pp. 1305‑1316.
2011 Kudlek AManfred Kudlek, A Relation Between Modal Logic and Language Closure Operators, Fund. Inform., v. 109, 2011, pp. 297‑304.
2011 SW AJeffrey Shallit, Ross Willard, Kuratowski’s Theorem for Two Closure Operators, arXiv:1109.1227 [math.GN],, 2011, 6 pp.
2010 BJZ AJanusz Brzozowski, Galina Jirásková, Chenglong Zou, Quotient Complexity of Closed Languages, Computer Science — Theory and Applications, Proceedings of the 5th International Computer Science Symposium in Russia, CSR 2010, Kazan, Russia, June 16‑20, 2010, Lecture Notes in Computer Science, v. 6072, edited by Farid Ablayev, Ernst W. Mayr, pp. 84‑95.
2010 Sherman ADavid Sherman, Variations on Kuratowski’s 14‑Set Theorem, Amer. Math. Monthly, v. 117 no. 2, 2010, pp. 113‑123.
2009 BGS‑a AJanusz Brzozowski, Elyot Grant, Jeffrey Shallit, Closures in Formal Languages and Kuratowski’s Theorem, arXiv:0901.3761 [cs.CC],, 2009, 12 pp.
2009 BGS‑b AJanusz Brzozowski, Elyot Grant, Jeffrey Shallit, Closures in Formal Languages and Kuratowski’s Theorem, Developments in Language Theory, 13th International Conference, DLT 2009, Lecture Notes in Computer Science, v. 5583, pp. 125‑144.
2009 BGS‑c AJanusz Brzozowski, Elyot Grant, Jeffrey Shallit, Closures in Formal Languages: Concatenation, Separation, and Algorithms, arXiv:0901.3763 [cs.CC],, Comp. Research Rep. — CORR, v. abs/0901.3, 2009, 12 pp.
2008 GJ AB. J. Gardner, Marcel Jackson, The Kuratowski Closure-Complement Theorem, New Zealand J. Math., v. 38, 2008, pp. 9‑44.
2006 GJ AAdam Grabowski, Magdalena Jastrzebska, Enhancing MML via Isomichi's Classification of Domains, Mech. Math. Appl., v. 5, 2006, pp. 11‑18.
2006 Grabowski AAdam Grabowski, Solving Two Problems in General Topology Via Types, Types for Proofs and Programs International Workshop, TYPES 2004, Jouy‑en‑Josas, France, December 15‑18, 2004, Revised Selected Papers, Lecture Notes in Computer Science, v. 3839, edited by Jean-Christophe Filliâtre, Christine Paulin-Mohring, Benjamin Werner, 2006, pp. 138‑153.
2005 Grabowski AAdam Grabowski, On the Computer-Checked Solution of the Kuratowski Closure-Complement Problem, Mech. Math. Appl., v. 4, 2005, pp. 25‑34.
2004 Farmer AFrank D. Farmer, Containment for c, s, t Operators on a Binary Relation, Algebra Universalis, v. 51, 2004, pp. 153‑175.
2004 JS AMarcel Jackson, Tim Stokes, Semilattice Pseudo-complements on Semigroups, Comm. Algebra, v. 32, 2004, pp. 2895‑2918.
2004 Jackson‑a AMarcel Jackson, Semilattices with Closure, Algebra Universalis, v. 52 no. 1, 2004, pp. 1‑37.
2004 Sherman ADavid Sherman, Variations on Kuratowski’s 14‑Set Theorem, arXiv:math/0405401 [math.GN],, 2004, 11 pp.
2003 BG ALilla Krystyna Baginska, Adam Grabowski, On the Kuratowski Closure-Complement Problem, J. Formal. Math., v. 15, 2003, pp. 1‑6.
2003 Brandsma AH. S. Brandsma, The Fourteen Subsets Problem: Interiors, Closures and Complements, Topology Explained, Topology Atlas, 2003, 4 pp.
2002 Voutsadakis AGeorge Voutsadakis, On Some Operations on Classes of Algebras and Coalgebras from a Bialgebraic Viewpoint,, 2002.
2001 MT ADragan Mašulović, Boža Tasić, Operators on Classes of Coalgebras, Theoret. Comput. Sci., v. 269, 2001, pp. 419‑431.
2001 Tasic ABoža Tasić, On the Partially Ordered Monoid Generated by the Operators H, S, P, Ps on Classes of Algebras, J. Algebra, v. 245, 2001, pp. 1‑19.
2000 WY AHe Wei, Zhang Yaoming, Interior and Boundary in a Locale, Adv. Math., v. 29, 2000, pp. 439‑443.
1999 GS AB. J. Gardner, Tim Stokes, Closure Rings, Comm. Math. Univ. Carolinae, v. 40 no. 3, 1999, pp. 413‑427.
1997 FW ATai‑He Fan, Guo‑Jun Wang, On Some Gross Misunderstandings About the Theory of Topological Molecular Lattices, Fuzzy Set. Syst., v. 90, 1997, pp. 61‑67.
1996 Pfaltz AJohn L. Pfaltz, Closure Lattices, Discrete Math., v. 154, 1996, pp. 217‑236.
1996 Shum AKar‑Ping Shum, Closure Functions on the Set of Positive Integers, Sci. China Ser. A, v. 39 no. 4, 1996, pp. 337‑346.
1995 GO‑a AEmmanuelle Garel, Jean Pierre Olivier, On Closures Verifying that the Interior of a Closed Element is Closed, Comm. Algebra, v. 23, 1995, pp. 3715‑3728.
1995 GO‑b AEmmanuelle Garel, Jean Pierre Olivier, The Opoid Generated by Transitive Closure and Interior and Symmetric Closure and Interior: A Characterization Using Generators and Relations, Rend. Sem. Mat. Univ. Poi. Torino, v. 53, 1995, pp. 71‑88.
1995 MT AM. S. Moslehian, N. Tavallaii, A Generalization of the Kuratowski Closure-Complement Problem, Punjab Univ. J. Math., v. 28, 1995, pp. 1‑9.
1995 Pfaltz AJohn L. Pfaltz, Evaluating the Binary Partition Function When N = 2^n, Cong. Num., v. 109, 1995, pp. 3‑12.
1993 GO AEmmanuelle Garel, Jean Pierre Olivier, About the Finiteness of Monoids Generated by Closures and Interiors, Semigroup Forum, v. 47, 1993, pp. 341‑352.
1993 Shum AKar‑Ping Shum, The Amalgamation of Closure and Boundary Functions on Semigroups and Partially Ordered Sets, Proceedings of the Conference on Ordered Structures and Algebra of Computer Languages: Hong Kong, 26‑29 June 1991, 1993, pp. 232‑243.
1988 Aull RC. E. Aull, Corrections and Additions for Classification of Topological Spaces II, Bull. Pol. Acad. Sci. Math., v. 40 no. 2, 1992, p. 175.
1992 KS AS. M. Kam, Kar‑Ping Shum, On a Problem of P. C. Hammer, Southeast Asian Bull. of Math., v. 16, 1992, pp. 123‑127.
1991 Fife AJames H. Fife, The Kuratowski Closure-Complement Problem, Math. Mag., v. 64 no. 3, 1991, pp. 180‑182.
1988 Aull AC. E. Aull, Classification of Topological Spaces II, Bull. Pol. Acad. Sci. Math., v. 36 no. 11-12, 1988, pp. 649‑654.
1988 Kuratowski AKazimierz Kuratowski, Selected Papers of Kazimierz Kuratowski, Sur l'Opération Ā de l'Analysis Situs (On the Topological Closure Operation), edited by Karol Borsuk, Ryszard Engelking, 1988, pp. 95‑112, in French.
1986 Wronski AStanislaw Wronski, On the Operations Definable in Terms of the Complementation and the Closure, Bull. Sect. Logic, Pol. Acad. Sci., v. 15, 1986, pp. 117‑121.
1984 Peleg AD. Peleg, A Generalized Closure and Complement Phenomenon, Discrete Math., v. 50, 1984, pp. 285‑293.
1984 Shum AKar‑Ping Shum, On the Boundary of Kuratowski 14‑Sets in Connected Spaces, Glas. Mat. Ser. III, v. 19, 1984, pp. 293‑296.
1982 Chagrov AA. V. Chagrov, Kuratowski Numbers, Appl. Funct. Anal. Approx. Th., 1982, pp. 186‑190, in Russian.
1982 Chagrov EA. V. Chagrov, Kuratowski Numbers, English translation by Mark Bowron, Math, 6 pp.
1982 Soltan AV. P. Soltan, Problems of Kuratowski Type, Mat. Issled., v. 65, 1982, pp. 121‑131, in Russian.
1982 Soltan EV. P. Soltan, Problems of Kuratowski Type, English translation by Mark Bowron, Math, 18 pp.
1981 Soltan AV. P. Soltan, On Kuratowski’s Problem, Bull. Acad. Pol. Sci., Sér. Sci. Math., v. 28, 1981, pp. 369‑375, in Russian.
1981 Soltan EV. P. Soltan, On Kuratowski’s Problem, English translation by Mark Bowron, Math, 11 pp.
1980 FP AM. J. Fischer, M. S. Paterson, The Fast Skew-Closure Algorithm, L'Enseign. Math., v. 26, 1980, pp. 345‑360.
1979 Soltan AV. P. Soltan, The Kuratowski Number of a Closure Space, IV Tiraspol Symposium on General Topology and its Applications, 1979, pp. 137‑139, in Russian.
1979 Soltan EV. P. Soltan, The Kuratowski Number of a Closure Space, English translation by Mark Bowron, Math, 1 p.
1978 Fishburn APeter C. Fishburn, Operations on Binary Relations, Discrete Math., v. 21, 1978, pp. 7‑22.
1977 Blok AW. J. Blok, The Free Closure Algebra on Finitely Many Generators, Ind. Math., v. 80, 1977, pp. 362‑379.
1977 Kleiner AĬ. Z. Kleĭner, Closure and Boundary Operators in Topological Spaces, Ukr. Math. J. (English), v. 29 no. 3, 1977, pp. 295‑296.
1977 Moser ALouise E. Moser, Closure, Interior, and Union in Finite Topological Spaces, Colloq. Math., v. 38, 1977, pp. 41‑51.
1975 BJ AJoel Berman, Steven L. Jordan, The Kuratowski Closure-Complement Problem, Amer. Math. Monthly, v. 82 no. 8, 1975, pp. 841‑842.
1975 SY AKar‑Ping Shum, K. W. Yip, On the Structure of Kuratowski Sets, J. Chin. Univ. Hong Kong, v. 3, 1975, pp. 429‑439.
1974 GE AYu. R. Gaida, A. É. Eremenko, On the Frontier Operator in Boolean Algebras with a Closure, Ukr. Math. J. (English), v. 26 no. 6, 1974, pp. 662‑664.
1974 Gol'dberg AA. A. Gol'dberg, On Boolean Algebras with a Derivation, Ukr. Math. J. (English), v. 26, 1974, pp. 365‑369.
1972 CJ AS. Comer, J. Johnson, The Standard Semigroup of Operators of a Variety, Algebra Universalis, v. 2, 1972, pp. 77‑79.
1972 GKM AR. L. Graham, D. E. Knuth, T. S. Motzkin, Complements and Transitive Closures, Discrete Math., v. 2, 1972, pp. 17‑29.
1972 Pigozzi AD. Pigozzi, On Some Operations on Classes of Algebras, Algebra Universalis, v. 2, 1972, pp. 346‑353.
1971 AS AJ. Anusiak, Kar‑Ping Shum, Remarks on Finite Topological Spaces, Colloq. Math., v. 23 no. 2, 1971, pp. 217‑223.
1971 Isomichi AYoshinori Isomichi, New Concepts in the Theory of Topological Space — Supercondensed Set, Subcondensed Set, and Condensed Set, Pacific J. Math., v. 38 no. 3, 1971, pp. 657‑668.
1971 Langford AEric Langford, Characterization of Kuratowski 14‑Sets, Amer. Math. Monthly, v. 78 no. 4, 1971, pp. 362‑367.
1967 Aull RC. E. Aull, Corrigendum: Classification of Topological Spaces, Bull. Acad. Pol. Sci., Sér. Sci. Math. Astron. Phys., v. 16 no. 6, 1968.
1968 Staley ADavid H. Staley, On the Commutativity of the Boundary and Interior Operators in a Topological Space, Ohio J. Sci., v. 68 no. 2, 1968, p. 84.
1967 Aull AC. E. Aull, Classification of Topological Spaces, Bull. Acad. Pol. Sci., Sér. Sci. Math. Astron. Phys., v. 15, 1967, pp. 773‑778.
1967 Coleman APatrick J. Coleman, On the Composition Semigroup Generated by Complement and an Expansive Function, Nieuw Arch. Wisk., v. 15, 1967, pp. 207‑210.
1967 Nelson AEvelyn Nelson, Finiteness of Semigroups of Operators in Universal Algebra, Canad. J. Math., v. 19, 1967, pp. 764‑768.
1966 HM AH. H. Herda, R. C. Metzler, Closure and Interior in Finite Topological Spaces, Colloq. Math., v. 15 no. 2, 1966, pp. 211‑216.
1966 Koenen AWilliam Koenen, The Kuratowski Closure Problem in the Topology of Convexity, Amer. Math. Monthly, v. 73 no. 7, 1966, pp. 704‑708.
1965 Hintikka AJ. Hintikka, A Closure and Complement Result for Nested Topologies, Fund. Math., v. 57 no. 1, 1965, pp. 97‑106.
1962 Chapman‑a AThomas A. Chapman, An Extension of the Kuratowski Closure and Complementation Problem, Math. Mag., v. 35 no. 1, 1962, pp. 31‑35.
1962 Chapman‑b AThomas A. Chapman, A Further Note on Closure and Interior Operators, Amer. Math. Monthly, v. 69 no. 6, 1962, pp. 524‑529.
1962 Hammer AP. C. Hammer, Extended Topology: Set-Valued Set-Functions, Nieuw Arch. Wisk., v. 10, 1962, pp. 55‑77.
1961 CM AHisashi Choda, Katuyosi Matoba, On a Theorem of Levine, Proc. Japan Acad., v. 37, 1961, pp. 462‑463.
1961 Levine ANorman Levine, On the Commutativity of the Closure and Interior Operators in Topological Spaces, Amer. Math. Monthly, v. 68 no. 5, 1961, pp. 474‑477.
1960 Hammer AP. C. Hammer, Kuratowski’s Closure Theorem, Nieuw Arch. Wisk., v. 8 no. 2, 1960, pp. 74‑80.
1955 Zarycki AMiron Zarycki, Boolean Algebras With a Closure and Boolean Algebras With a Derivation, Dop. Akad. Nauk. Ukrain., v. 1, 1955, pp. 3‑6, in Ukrainian.
1954 Halfar AEdwin Halfar, The Isolated Points of a Set, Port. Math., v. 13 no. 3, 1954, pp. 125‑128.
1951 Halfar AEdwin Halfar, A Note on Point-Set Operators, Port. Math., v. 10 no. 2, 1951, pp. 103‑104.
1949 Zarycki AMiron Zarycki, On an Operation in the Theory of Point Sets, Nauk. Zap. Ser. Fiz.‑Mat., v. 12 no. 3, 1949, pp. 35‑43, in Ukrainian.
1947 Zarycki AMiron Zarycki, Some Properties of the Notion of Derived Set in Abstract Spaces, Nauk. Zap. Ser. Fiz.‑Mat., v. 5 no. 1, 1947, pp. 22‑33, in Ukrainian.
1944 MT AJ. C. C. McKinsey, Alfred Tarski, The Algebra of Topology, Ann. of Math., v. 45, 1944, pp. 141‑191.
1943 Hewitt AEdwin Hewitt, A Problem of Set-Theoretic Topology, Duke Math. J., v. 10 no. 2, 1943, pp. 309‑333.
1941 Chittenden‑a AE. W. Chittenden, A New Proof of a Formula of Kuratowski, Proc. Iowa Acad. Sci., v. 48, 1941, pp. 299‑300.
1941 Chittenden‑b AE. W. Chittenden, On the Reduction of Topological Functions, Lectures in Topology: The University of Michigan Conference of 1940, edited by William L. Ayres, Raymond L. Wilder, 1941, pp. 267‑285.
1941 Haight AFrank Haight, On the Independence of Operators on a Lattice, Proc. Iowa Acad. Sci., v. 48, 1941, pp. 301‑304.
1941 McKinsey AJ. C. C. McKinsey, A Solution of the Decision Problem for the Lewis Systems S2 and S4, With an Application to Topology, J. Symbol. Logic, v. 6 no. 4, 1941, pp. 117‑134.
1939 Stopher AE. C. Stopher Jr., Point Set Operators and Their Interrelations, Bull. Amer. Math. Soc., v. 46, 1939, pp. 758‑762.
1937 Sanders ASamuel T. Sanders Jr., Functional Equations Defining the Complementary Operations, Natl. Math. Mag., v. 12 no. 3, 1937, pp. 115‑117.
1937 Stopher AE. C. Stopher Jr., Cyclic Relations in Point Set Theory, Bull. Amer. Math. Soc., v. 43, 1937, pp. 686‑694.
1936 Sanders ASamuel T. Sanders Jr., Derived Sets and Their Complements, Bull. Amer. Math. Soc., v. 42, 1936, pp. 577‑584.
1930 Zarycki AMiron Zarycki, Über den Kern einer Menge (On the Core of a Set), Jahr. Deutsch. Math. Ver., v. 39, 1930, pp. 154‑158, in German.
1928 Zarycki‑a AMiron Zarycki, Allgemeine Eigenschaften der Cantorschen Kohärenzen (General Properties of Cantor's Coherences), Trans. Amer. Math. Soc., v. 30 no. 3, 1928, pp. 498‑506, in German.
1928 Zarycki‑b AMiron Zarycki, Derivation and Coherence in Abstract Sets, Zb. Mat.‑Prir.‑Likar. Sekt. Nauk. Tov., v. 27, 1928, pp. 247‑259, in Ukrainian.
1927 Zarycki AMiron Zarycki, Quelques Notions Fondamentales de l'Analysis Situs au Point du Vue de l'Algèbre de la Logique (Some Fundamental Concepts of Topology in Terms of the Algebra of Logic), Fund. Math., v. 9, 1927, pp. 3‑15, in French.
1927 Zarycki EMiron Zarycki, Quelques Notions Fondamentales de l'Analysis Situs au Point du Vue de l'Algèbre de la Logique (Some Basic Topological Concepts in Terms of the Algebra of Logic), English translation by Mark Bowron, Math, 8 pp.
1922 Kuratowski AKazimierz Kuratowski, Sur l'Opération Ā de l'Analysis Situs (On the Topological Closure Operation), Fund. Math., v. 3, 1922, pp. 182‑199, in French.
1922 Kuratowski EKazimierz Kuratowski, Sur l'Opération Ā de l'Analysis Situs (On the Topological Closure Operation), English translation by Mark Bowron, Math, 11 pp.




2012 AB PAlex Aguado, Closures and Complements, Problem 1888, Math. Mag., v. 85 no. 1, 2012, p. 62, Solution: Mark Bowron, v. 86 no. 1, 2013, pp. 67‑68.
2012 BB PMark Bowron, More on Kuratowski 14‑Sets, Problem 1898, Math. Mag., v. 85 no. 3, 2012, p. 228, Solution: Bruce S. Burdick, v. 86 no. 3, 2013, p. 231.
2004 BB PMark Bowron, Closure, Complement, and Union, Problem 11059, Amer. Math. Monthly, v. 111 no. 1, 2004, pp. 64‑65, Solution: Bruce Burdick, v. 113 no. 1, 2006, p. 83.
1997 BRR PMark Bowron, Stanley Rabinowitz, Closure, Complement, and Arbitrary Union, Problem 10577, Amer. Math. Monthly, v. 104 no. 2, 1997, p. 169, Solution: John Rickard, v. 105 no. 3, 1998, pp. 282‑283.
1986 BF PEdwin Buchman, Generating Sets in a Topological Space, Problem E3144, Amer. Math. Monthly, v. 93 no. 4, 1986, p. 299, Solution: Jesús Ferrer, v. 95 no. 4, 1988, p. 353.
1979 LM PEric Langford, Sets Formed by Iterated Closure, Interior, and Union, Problem 6260, Amer. Math. Monthly, v. 86 no. 3, 1979, p. 226, Solution: William Myers, v. 87 no. 8, 1980, pp. 680‑681.
1974 SY PArthur Smith, Kuratowski Sets, Problem 5996, Amer. Math. Monthly, v. 81 no. 9, 1974, p. 1034, Solution: Chie Y. Yu, v. 85 no. 4, 1978, pp. 283‑284.
1969 Shum PKar‑Ping Shum, Bounds on the Kuratowski Family, Problem 153, Can. Math. Bull., v. 12 no. 2, 1969, p. 237, Solution: K. P. Shum, v. 14 no. 4, 1971, pp. 602‑603.
1968 BL PStephen Baron, Kuratowski’s 14‑Sets, Problem 5569, Amer. Math. Monthly, v. 75 no. 2, 1968, p. 199, Solution: Eric Langford, v. 78 no. 4, 1971, p. 411.
1966 KM PWilliam Koenen, On Two Closure Problems, Problem E1941, Amer. Math. Monthly, v. 73 no. 10, 1966, p. 1123, Solution: L. F. Meyers, v. 75 no. 4, 1968, pp. 408‑409.
1965 LM PS. P. Lloyd, A Kuratowski Closure and Complement Problem, Problem 5349, Amer. Math. Monthly, v. 72 no. 10, 1965, p. 1136, Solution: J. C. Morgan II, v. 73 no. 10, 1966, pp. 1132‑1134.

2017 SA QDistinct Sets in Topology?, studyAcer, 2017.
2016 AM QArkanj3l, mathematrucker, Which math books title every problem/exercise?, reddit, 2016.
2016 BDMSS Qbof, Did, Saaqib Mahmuud, sinbadh, Martin Sleziak, Prob. 21, Sec. 17 in Munkres’ TOPOLOGY, 2nd ed: Closure and Complementation Can Result in at Most 14 Different Sets, Stack Exchange, 2016.
2016 RSSU Qrschwieb, Brian M. Scott, Slade, user43208, Moore Closure and Realizing the Kuratowski Monoid, Stack Exchange, 2016.
2015 AGMU Qanakhronizein, Dejan Govc, mathematrucker, user210387, Does There Exist a Kuratowski Set Which is Uncountable?, Stack Exchange, 2015.
2015 AMNPS QArthur,, J.‑E. Pin, SamM, Playing With Closure and Interior to Get the Maximum Number of Sets, Stack Exchange, 2015.
2015 Anonymous QAnonymous, Kuratowski’s Closure Complement Problem,, 2015.
2015 DKPST QDontknowanything, Arpit Kansal, phaiakia, Brian M. Scott, Tom‑Tom, Need a Counterexample Related to Interior and Closure, Stack Exchange, 2015.
2015 MSU Qmathematrucker, Martin Sleziak, User23, Variations of Kuratowski Closure Complement Theorem, Stack Exchange, 2015.
2015 MU Qmathematrucker, User23, Classifying Topological Spaces by Kuratowski Monoid, Stack Exchange, 2015.
2015 OEWM Qoctatoan, endymion32, whirligig231, mathematrucker, The Kuratowski closure‑complement problem (very fun and not really topological), reddit, 2015.
2014 AACMMSU QMichael Albanese, arjafi, Andrés E. Caicedo, Saaqib Mahmuud, mathematrucker, Martin Sleziak, user45765, A Question on the Proof of 14 Distinct Sets Can Be Formed by Complementation and Closure, Stack Exchange, 2014.
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2014 CMU QMario Carneiro, mathematrucker, user134824, How Many Sets Can You Get by Taking Closures, Complements, and Intersections?, Stack Exchange, 2014.
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2013 ACFM QAshot, Haskell Curry, Arthur Fischer, mathematrucker, How to Prove That int(cl(A)) = cl(int(A))?, 2013.
2013 BC QB11, Haskell Curry, Example of a Set That Satisfies the Upper Bound in the Kuratowski Closure‑Complement Theorem, Stack Exchange, 2013.
2013 BCGJKKMMUV QHenno Brandsma, Andrés E. Caicedo, Glougloubarbaki, Jared, kahen, Asaf Karagila, mathematrucker, mvcouwen, user64494, How Many Sets Can We Get by Taking Interiors and Closures?, Stack Exchange, 2013.
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2012 DMMV QJason DeVito, Arturo Magidin, David Mitra, Voldemort, Is the Interior of a Set Always Equal to the Interior of its Closure?, Stack Exchange, 2012.
2012 FGJMM QArthur Fischer, Dejan Govc, John, mathematrucker, Gerry Myerson, What is the Smallest Cardinality of a Kuratowski 14‑Set?, Stack Exchange, 2012.
2012 MSSU QDylan Moreland, Brian M. Scott, Sigur, user31899, Closure of the Interior of Another Closure, Stack Exchange, 2012.
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2011 AM QAdelle, mars, Distinct Sets in the Usual Topology of R, Topology Q+A Board, Ask a Topologist 2011.
2011 BL QBeni Bogosel, Zhen Lin, Why Some People Don't Like Proofs by Contradiction, Stack Exchange, 2011.
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2010 AM Qanonymous, Austin Mohr, Funny Identities, Stack Exchange, 2010.
2010 CCMY QS. Carnahan, Zev Chonoles, mathematrucker, Qiaochu Yuan, Kuratowski Closure-Complement Problem for Other Mathematical Objects?, MathOverflow, 2010.
2010 DHMM QFrançois G. Dorais, Joel David Hamkins, mathematrucker, Greg Muller, The Closure-Complement-Intersection Problem, MathOverflow, 2010.
2010 MMST Qmathematrucker, me@home, statham, t0rajir0u, Closure; Closed Set and Open Set, Art of Problem Solving, 2010.
2008 Brandsma QH. S. Brandsma, Topology, Kuratowski Problem, Topology Q+A Board, Ask a Topologist 2008.
2005 BGMS QRussell Blackadar, George Greene, mitch, Jim Sprigs, "Separate Entity" and Individuation in Mathematics, The Math Forum, 2005.
2005 BS QClaudio Buffara, Paul Santa Rita, Problema do Kuratowski (Kuratowski’s Problem), 2005, in Portuguese.
2005 CHOR QGeorge Cox, Stephen J. Herschkorn, Michael Orion, Keith Ramsay, Why 14 is an Interesting Number (Topology), The Math Forum, 2005.
2005 EM QWilliam Elliot, mitch, 14 Sets, 14 Modalities, Epistemic Logic, Cantor Spaces and an Euler Tour, The Math Forum, 2005.
2004 Mitch Qmitch, The Anticlassicalist }{ : Mitchism for Daleks, The Math Forum, 2004.
2002 LRT QMoufang Loop, Dave Rusin, Bill Taylor, Operators and Saltus, The Math Forum, 2002.
2001 KKR QKathleen, Andres Koropecki, Dave L. Renfro, Looking for a Subset of R that .... , The Math Forum, 2001.
1999 Bowron QMark Bowron, New Kuratowski Closure-Complement (and Union) Results?, The Math Forum, 1999.
1998 DGM QJulian Dontchev, Fred Galvin, David McIntyre, How Many Sets are Generated by Closure, Union and Complement?, The Math Forum, 1998.
1997 BHHPV QH. S. Brandsma, Kjetil Helstrup, Jeffrey C. Humpherys, Barry Paul, Valerio Venturi, Closure and Complement Give Only 14 Different Sets, The Math Forum, 1997.
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2012 Medina WMiguel A. M. Medina, El Teorema Clausura-Complemento de Kuratowski (Kuratowski’s Closure-Complement Theorem), Gaussian, 2012, in Spanish.
2012 Pfaltz WJohn L. Pfaltz, Closure Spaces: A Brief Overview, 2012.
2011 FB WKuratowski Closure-Complement Theorem, Facebook, 2011.
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2010 ElJj WEl Jj, Fermeture ou Complémentaire? (Closure or Complement?), Canalblog, 2010, in French.
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2007 Mathematrucker Wmathematrucker, Kuratowski’s Closure-Complement Problem, Wikipedia, 2007.
2007 Nadish WNadish, Combining Interior, Complement, and Closure Operators, The Knot Atlas, 2007.
2003 FK WAlex Fink, Egil Kvaleberg et al., 14 (number), Wikipedia, 2003.
2000 BW WMark Bowron, Eric W. Weisstein, Kuratowski’s Closure-Complement Problem, MathWorld — A Wolfram Web Resource, 2000.
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2016 Jiaying TShen Jiaying, 14 Set Problem and Its Related Topics, 2016, in Chinese.
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Kuratowski Closure-Complement Cornucopia
Kuratowski’s Closure-Complement Cornucopia

There is a large and scattered literature on Kuratowski’s theorem, most of which focuses on topological spaces; an admirable survey is the paper of Gardner and Jackson [2008 GJ AB. J. Gardner, Marcel Jackson, The Kuratowski Closure-Complement Theorem, New Zealand J. Math., v. 38, 2008, pp. 9‑44.].
—Janusz Brzozowski, Elyot Grant, and Jeffrey Shallit [2009 BGS‑a AJanusz Brzozowski, Elyot Grant, Jeffrey Shallit, Closures in Formal Languages and Kuratowski’s Theorem, arXiv:0901.3761 [cs.CC],, 2009, 12 pp.]

After completing his Ph.D. at the University of Warsaw in 1921, Kazimierz Kuratowski published the first part of his dissertation one year later in the Polish journal Fundamenta Mathematicae [1922 Kuratowski AKazimierz Kuratowski, Sur l’Opération Ā de l’Analysis Situs (On the Topological Closure Operation), Fund. Math., v. 3, 1922, pp. 182‑199, in French. (in French)], [2012 Kuratowski EKazimierz Kuratowski, Sur l’Opération Ā de l’Analysis Situs (On the Topological Closure Operation), English translation by Mark Bowron, Math, 2012, 11 pp. (English)].

Kuratowski’s oft‑cited paper taught us something new about the number 14:

Whenever one subset in a topological space has closure and complement applied to it repeatedly (in any order), the number of distinct subsets generated is always less than or equal to 14.

To become famous, it helps to have a name. Kuratowski’s off-the-wall discovery got its lucky break when John L. Kelley took the rare step of naming every problem in his classic textbook [1955 Kelley BJohn L. Kelley, General Topology, 1955, p. 57.]; our present-day cornucopia would surely contain less fruit had he not. Kelley gave Kuratowski’s result the fitting name Kuratowski Closure and Complementation Problem.

Kelley’s choice (or minor variations of it) stuck for nearly half a century. The numeral 14, or word fourteen, did not appear in titles until the early twenty-first century [2003 Brandsma AH. S. Brandsma, The Fourteen Subsets Problem: Interiors, Closures and Complements, Topology Explained, Topology Atlas, 2003, 4 pp.], [2005 Muhm DPhilip Muhm, Kuratowski’s 14‑Set Theorem — A Modal Logic View, 2005, 58 pp.], [2007 Beckman MRyan T. Beckman, Basic Topology and the Kuratowski 14‑set Problem, 2007, 70 pp.], [2010 Sherman ADavid Sherman, Variations on Kuratowski’s 14‑Set Theorem, Amer. Math. Monthly, v. 117 no. 2, 2010, pp. 113‑123.]. It did not appear in the theorem’s name until 1997, in a paper on topological molecular lattices [1997 FW ATai‑He Fan, Guo‑Jun Wang, On Some Gross Misunderstandings About the Theory of Topological Molecular Lattices, Fuzzy Set. Syst., v. 90, 1997, pp. 61‑67.]: “The Kuratowski 14 set theorem is true: Let A be an element in a symmetric TML, then, by using alternatively interior, pseudocomplement and closure to A can give at most 14 different sets.” (italics mine)

It next appeared in 1998, in an editor’s note following the published solution to Monthly Problem 10577 [1997 BRR PMark Bowron, Stanley Rabinowitz, Closure, Complement, and Arbitrary Union, Problem 10577, Amer. Math. Monthly, v. 104 no. 2, 1997, p. 169, Solution: John Rickard, v. 105 no. 3, 1998, pp. 282‑283.]: “Previous Monthly problems related to the 14 sets problem  include 5569 [1968 BL PStephen Baron, Kuratowski’s 14‑Sets, Problem 5569, Amer. Math. Monthly, v. 75 no. 2, 1968, p. 199, Solution: Eric Langford, v. 78 no. 4, 1971, p. 411.], 5996 [1974 SY PArthur Smith, Kuratowski Sets, Problem 5996, Amer. Math. Monthly, v. 81 no. 9, 1974, p. 1034, Solution: Chie Y. Yu, v. 85 no. 4, 1978, pp. 283‑284.], and 6260 [1979 LM PEric Langford, Sets Formed by Iterated Closure, Interior, and Union, Problem 6260, Amer. Math. Monthly, v. 86 no. 3, 1979, p. 226, Solution: William Myers, v. 87 no. 8, 1980, pp. 680‑681.].” (italics mine)

During the 1980s and early 1990s the Monthly’s lag time from proposal to published solution gradually inflated to nearly four years. Intent on slashing this during his 1996‑2002 tenure as lead editor, Daniel Ullman — the “Paul Volcker of problem editors” — routinely packed as many solutions as possible into each issue. Thus he would have strongly favored abbreviations, especially during the earlier part of his tenure when the note was written. However his thinking went, it is doubtful Ullman intended to tinker with the established name.

Those first two appearances of 14 set in place of closure-complement were not trendsetting. However, five years later, not only did fourteen subsets problem appear in a paper that was freely available on the web [2003 Brandsma AH. S. Brandsma, The Fourteen Subsets Problem: Interiors, Closures and Complements, Topology Explained, Topology Atlas, 2003, 4 pp.], it appeared in the title of that paper. This was a game changer: the new name spread quickly.

The following year, David Sherman claimed — with no support from his thirteen references (Kelley would have made a nice fourteenth) — that Kuratowski’s result is known as the 14‑set theorem. Sherman’s misstatement appeared in both his Monthly article [2010 Sherman ADavid Sherman, Variations on Kuratowski’s 14‑Set Theorem, Amer. Math. Monthly, v. 117 no. 2, 2010, pp. 113‑123.] and its 2004 arXiv preprint. Six coauthors of a more recent paper [2015 BCMPRS AT. Banakh, O. Chervak, T. Martynyuk, M. Pylypovych, A. Ravsky, M. Simkiv, Kuratowski monoids of n‑topological spaces, arXiv:1508.07703v1 [math.GN],, 2015, 20 pp.] employed a shotgun approach, calling it “the famous 14‑set closure‑complement Theorem of Kuratowski.”

In these pages Math Transit chronicles the abundance of literature related to — Kelley’s — Kuratowski Closure‑Complement Theorem.

updated 27 June 2017
by mathematrucker
mathematrucker smiley
[portmanteau above]

© 2012-2017 mathematrucker