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A334253
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Number of strict closure operators on a set of n elements which satisfy the T_0 separation axiom.
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2
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OFFSET
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0,3
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COMMENTS
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The T_0 axiom states that the closure of {x} and {y} are different for distinct x and y.
A closure operator is strict if the empty set is closed.
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LINKS
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FORMULA
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EXAMPLE
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The a(0) = 1 through a(2) = 3 set-systems of closed sets:
{{}} {{1},{}} {{1,2},{1},{}}
{{1,2},{2},{}}
{{1,2},{1},{2},{}}
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CROSSREFS
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The number of all strict closure operators is given in A102894.
For all T0 closure operators, see A334252.
For strict T1 closure operators, see A334255.
A strict closure operator which preserves unions is called topological, see A001035.
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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