doc-src/TutorialI/Misc/document/arith4.tex

added state: 'a * 'b -> 'a * ('a * 'b);

\begin{isabelle}%
\isacommand{lemma}~{"}{\isasymnot}~m~<~n~{\isasymand}~m~<~n+1~{\isasymLongrightarrow}~m~=~n{"}\isanewline
\end{isabelle}%