Is $A - B = \emptyset$? $A = \{1,2,3,4,5\}, B = \{1,2,3,4,5,6,7,8\}$
$A - B =$ ?
Does that just leave me with $\emptyset$?  Or do I do something with the leftover $6,7,8$?

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