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\begin{document}

\title[101 Homework \#23]{Math 101: Algebra I \\ Homework, Day \#23}
\date{Assigned Wednesday, 19 October 2016; due Friday, 21 October 2016}

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\vspace{1ex}

\begin{problab}{JV23.A} 
Let $R$ be a ring, and let $D,L,M,N$ be $R$-modules.  Show that if 
\[ 0 \to L \xrightarrow{\psi} M \xrightarrow{\phi} N \]
is exact, then
\[ \Hom_R(D,L) \xrightarrow{\psi_*} \Hom_R(D,M) \xrightarrow{\phi_*} \Hom_R(D,N) \]
is exact.  \emph{[Hint: check your work using Theorem \textup{28}.]}
\end{problab}

\end{document}