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\begin{document}
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{\bf Math 999 Homework 14\\}
Jane Doe\\
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\begin{enumerate}
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\item[(2.1.5)] \emph{Show that every natural number is interesting.}
\begin{proof}
  Suppose not.  Then the set $E \subset \N$ of uninteresting natural
  numbers is nonempty, and therefore it contains a minimal
  element $n$.  Equivalently $n$ is the smallest uninteresting
  natural number.  But that is a rather interesting property, hence $n \notin E$,
  a contradiction.
\end{proof}

\end{enumerate}

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