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$A = \{1,2,3,4,5\}, B = \{1,2,3,4,5,6,7,8\}$

$A - B =$ ?

Does that just leave me with $\emptyset$? Or do I do something with the leftover $6,7,8$?

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Yes, it is empty. Not that it's $\emptyset$, and not $\{\emptyset\}$ here. –  1015 Feb 7 '13 at 16:45
    
Fantastic, thanks! –  KKendall Feb 7 '13 at 16:48
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1 Answer

up vote 4 down vote accepted

$A - B = \emptyset$, because by definition, $A - B$ is everything that is in $A$ but not in $B$.

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