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\pdftitle{Set Difference}
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\subsection*{Set Difference}
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For any sets $S$ and $T$, the set $S :\: T$ consists of all elements
of $S$ that are not elements of $T$.  For example, 
  $\{1, 3, 5 \} :\: \{0, 3, 6\}$ equals $\{1, 5\}$; and $Nat :\: \{0\}$ 
consists of the set of all elements of $Nat$ (the set of natural
numbers) except $0$.
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