Added tag Isabelle2019-RC4 for changeset ad2d84c42380
(*<*)theory fakenat imports Main begin(*>*)text\<open>\noindentThe type \tydx{nat} of naturalnumbers is predefined to have the constructors \cdx{0} and~\cdx{Suc}.It behaves approximately as if it were declared like this:\<close>datatype nat = zero ("0") | Suc nat(*<*)end(*>*)