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% \MRhref is called by the amsart/book/proc definition of \MR.
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\begin{thebibliography}{{Abr}13}

\bibitem[{Abr}13]{Moduli}
D.~{Abramovich}, \emph{{Moduli of algebraic and tropical curves}}, ArXiv
  e-prints (2013).

\bibitem[ACP12]{ACP}
D.~{Abramovich}, L.~{Caporaso}, and S.~{Payne}, \emph{{The tropicalization of
  moduli space}}.

\end{thebibliography}