\def\cprime{$'$}
\begin{thebibliography}{1}

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Nicolas Bourbaki.
\newblock {\em Theory of sets}.
\newblock Elements of Mathematics (Berlin). Springer-Verlag, Berlin, 2004.
\newblock Reprint of the 1968 English translation [Hermann, Paris; MR0237342].

\bibitem{Cartmell0}
John Cartmell.
\newblock Generalised algebraic theories and contextual categories.
\newblock {\em Ph.D. Thesis, Oxford University}, 1978.
\newblock \url{http://www.cs.ru.nl/~spitters/Cartmell.pdf}.

\bibitem{Cartmell1}
John Cartmell.
\newblock Generalised algebraic theories and contextual categories.
\newblock {\em Ann. Pure Appl. Logic}, 32(3):209--243, 1986.

\bibitem{Lawvere}
F.~William Lawvere.
\newblock Functorial semantics of algebraic theories and some algebraic
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\newblock {\em Repr. Theory Appl. Categ.}, (5):1--121, 2004.
\newblock Reprinted from Proc. Nat. Acad. Sci. U.S.A. {{\bf{5}}0} (1963),
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\bibitem{Cfromauniverse}
Vladimir Voevodsky.
\newblock A {C}-system defined by a universe category.
\newblock {\em Theory Appl. Categ.}, 30(37):1181--1215, 2015.
\newblock \url{http://www.tac.mta.ca/tac/volumes/30/37/30-37.pdf}.

\bibitem{Csubsystems}
Vladimir Voevodsky.
\newblock Subsystems and regular quotients of {C}-systems.
\newblock In {\em A panorama of mathematics: pure and applied}, volume 658 of
  {\em Contemp. Math.}, pages 127--137. Amer. Math. Soc., Providence, RI, 2016.
\newblock prepublication version in \url{http://arxiv.org/abs/1406.7413}.

\end{thebibliography}