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Key Concept
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Closure property
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When you combine any two elements of the set, the result is also included in the set.
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$\"\"$

Select two different natural numbers and then determine whether

the subtraction is a natural number.

Try some examples.

4 $\"\"$ 5 = $\"\"$ 1.

This is not a natural number, so the set of natural numbers is not closed

under subtraction. $\"\"$

The set of natural numbers is not closed under subtraction.

\ Key Concept \	\ Closure property \
\ When you combine any two elements of the set, the result is also included in the set. \