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Om Closure (mathematics)
High Quality Content by WIKIPEDIA articles! In mathematics, a set is said to be closed under some operation if performance of that operation on members of the set always produces a unique member of the same set. For example, the real numbers are closed under subtraction, but the natural numbers are not: 3 and 8 are both natural numbers, but the result of 3 aE ' 8 is not. 0 is a closed set under multiplication.