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\homework{4: The (false) Four-Color Theorem}{Due Tuesday, week 5, at the start of class}


\section*{Checkdown/also extra-credit problem.}

This week is like last week!  To get credit for this problem, just work on it; i.e. think about it, write down ideas, and otherwise spend a hour or two trying to figure out what's going on.  Assignments that show effort (i.e. $>1/2$ page of work and writing, coherent thoughts, good questions for me) will get credit.  If you fully answer the problem, you get the extra-credit half-point as well!

\begin{enumerate}
\item Find the flaw in the proof we gave in class!  In other words: explain why the proof in class is mistaken, omits some cases, or otherwise makes a conclusion that is unwarranted.
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