References for OCaml, Scheme, and proper tail recursion.

thesis.tex

@@ -881,6 +881,14 @@ bindings, pair deconstructing, and case splitting. In each of those
 cases we subtract the relevant binder(s) from the set of free
 variables.
 
+\paragraph{Proper tail-recursion}
+
+Many industrial-strength functional programming languages such as
+SML~\cite{MilnerTHM97}, OCaml~\cite{LeroyDFGRV20},
+Scheme~\cite{SperberDFSFM10} rely heavily on being properly
+tail-recursive\dots
+\dhil{TODO define properly tail-recursive}
+
 \subsection{Typing rules}
 \label{sec:base-language-type-rules}
 %