doc-src/TutorialI/Misc/arith4.thy

tidied, proving gcd_greatest_iff and using induct_tac

(*<*)
theory arith4 = Main:;
(*>*)
lemma "\\<not> m < n \\<and> m < n+1 \\<Longrightarrow> m = n";
(**)(*<*)
by(arith);
end
(*>*)