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\documentclass{math215}
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\usepackage{times,txfonts}

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\doclabel{Math 215: Homework 14}
\docauthor{Your name here}
\docdate{May 1, 2012}
\input{math215extras.tex}
\begin{document}
  
\begin{proposition}{13.A} Suppose $A$ is uncountable and
  $A\subseteq B$.  Then $B$ is uncountable.
\end{proposition}

\begin{proposition}{13.B} $\{a+\sqrt{2}b:a,b\in\Rats\}$ is countable.
\end{proposition}

\begin{proposition}{13.28} Every open interval $(a,b)$ has
  the same cardinality as $\Reals$.
\end{proposition}


\end{document}