explicit theory qualifier for session "HOL-Proofs": its theory name space overlaps with session "HOL", even for further imports;
(*<*)
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 approximately as if it were declared like this:
*}
datatype nat = zero ("0") | Suc nat
(*<*)
end
(*>*)