modifying the depth-limited compilation to be sound, but now throws an error undefined in case of hitting the depth limit in an negative context; cleaning up the examples
(*<*)
theory fakenat imports Main begin;
(*>*)
text{*\noindent
The type \tydx{nat} of natural
numbers is predefined to have the constructors \cdx{0} and~\cdx{Suc}. It behaves as if it were declared like this:
*}
datatype nat = 0 | Suc nat
(*<*)
end
(*>*)