doc-src/TutorialI/Misc/arith3.thy

avoid referencing thy value;
rename_numerals: use implicit theory context;
eliminated some simpset_of Int.thy (why needed anyway?);

(*<*)
theory arith3 = Main:;
(*>*)
lemma "n*n = n \\<Longrightarrow> n=0 \\<or> n=1";
(**)(*<*)
oops;
end
(*>*)