doc-src/Main/Docs/Main_Doc.thy

 \begin{tabular}{@ {} l @ {\quad$\equiv$\quad} l @ {}}
 @{term"fun_upd f x y"} & @{term[source]"fun_upd f x y"}\\
 @{text"f(x\<^isub>1:=y\<^isub>1,\<dots>,x\<^isub>n:=y\<^isub>n)"} & @{text"f(x\<^isub>1:=y\<^isub>1)\<dots>(x\<^isub>n:=y\<^isub>n)"}\\
 \end{tabular}
 
+
+\section{Hilbert\_Choice}
+
+Hilbert's selection ($\varepsilon$) operator: @{term"SOME x. P"}.
+\smallskip
+
+\begin{tabular}{@ {} l @ {~::~} l @ {}}
+@{const Hilbert_Choice.inv_onto} & @{term_type_only Hilbert_Choice.inv_onto "'a set \<Rightarrow> ('a \<Rightarrow> 'b) \<Rightarrow> ('b \<Rightarrow> 'a)"}
+\end{tabular}
+
+\subsubsection*{Syntax}
+
+\begin{tabular}{@ {} l @ {\quad$\equiv$\quad} l @ {}}
+@{term inv} & @{term[source]"inv_onto UNIV"}
+\end{tabular}
 
 \section{Fixed Points}
 
 Theory: @{theory Inductive}.