-\glspl{GADT}. Listing~\ref{lst:exdeepgadt} shows the same language, but
-type-safe with a \gls{GADT}\footnote{Note that \glspl{GADT} are not supported
-in \gls{Clean}. They can be simulated using bimaps}\todo{cite}. Unfortunately
-the lack of extendability stays a problem. If a language construct is added no
+\glspl{GADT}\cite{cheney_first-class_2003}. Listing~\ref{lst:exdeepgadt} shows
+the same language, but type-safe with a \gls{GADT}. \glspl{GADT} are not
+supported in the current version of \gls{Clean} and therefore the syntax is
+artificial. However, it has been shown that \glspl{GADT} can be simulated using
+bimaps or projection pairs\cite{cheney_lightweight_2002}. Unfortunately the
+lack of extendability remains a problem. If a language construct is added, no