Which set is closed under subtraction?

A set is closed under subtraction if subtracting any two numbers in it always gives a number in the same set. The difference of two rational numbers is rational; for example, 3/4 − 1/2 = 1/4. Whole numbers and natural numbers can give negative results, and irrational numbers can give rational results, such as √2 − √2 = 0. Therefore, the set of rational numbers is closed under subtraction.

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