1
\begin{isabelle}%
2
\isacommand{lemma}~{"}min~i~(max~j~(k*k))~=~max~(min~(k*k)~i)~(min~i~(j::nat)){"}\isanewline
3
\isacommand{apply}(arith)\isacommand{.}\isanewline
4
\end{isabelle}%