proper context option: change of underlying Options.default will not survive PIDE "Prover.options" (e.g. change of Isabelle/jEdit plugin options);
(*<*)
theory Plus imports Main begin
(*>*)
text\<open>\noindent Define the following addition function\<close>
primrec add :: "nat \<Rightarrow> nat \<Rightarrow> nat" where
"add m 0 = m" |
"add m (Suc n) = add (Suc m) n"
text\<open>\noindent and prove\<close>
(*<*)
lemma [simp]: "\<forall>m. add m n = m+n"
apply(induct_tac n)
by(auto)
(*>*)
lemma "add m n = m+n"
(*<*)
by(simp)
end
(*>*)