renamed kill_all to kill, in conformance with atp_kill command;
simplified/unified treatment of preferences;
check_thread_manager: CRITICAL due to global ref;
goal addressing via Thm.cprem_of;
reduced NJ basis library stuff to bare minimum;
(*<*)
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
(*>*)