simplified/refined document model: collection of named nodes, without proper dependencies yet;
moved basic type definitions for ids and edits from Isar_Document to Document;
removed begin_document/end_document for now -- nodes emerge via edits;
edits refer to named nodes explicitly;
(*<*)
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
(*>*)