diff -r 603df40ef1e9 -r 1d1d9f60c29b doc-src/TutorialI/Inductive/even-example.tex --- a/doc-src/TutorialI/Inductive/even-example.tex Fri Feb 16 18:50:09 2001 +0100 +++ b/doc-src/TutorialI/Inductive/even-example.tex Fri Feb 16 18:51:19 2001 +0100 @@ -142,8 +142,7 @@ To conclude, we tell Isabelle that the desired value is \isa{Suc\ k}. With this hint, the subgoal falls to \isa{simp}. \begin{isabelle} -\isacommand{apply}\ (rule_tac\ x\ =\ "Suc\ k"\ \isakeyword{in}\ exI, -\isacommand{apply}\ simp) +\isacommand{apply}\ (rule_tac\ x\ =\ "Suc\ k"\ \isakeyword{in}\ exI, simp) \end{isabelle} @@ -164,8 +163,8 @@ Before applying induction, we typically must generalize the induction formula. With rule induction, the required generalization can be hard to find and sometimes requires a complete reformulation of the -problem. In this example, the obvious statement of the result is not -inductive: +problem. In this example, our first attempt uses the obvious statement of +the result. It fails: % \begin{isabelle} \isacommand{lemma}\ "Suc\ (Suc\ n)\ \isasymin \ even\ @@ -206,7 +205,7 @@ Using our lemma, we can easily prove the result we originally wanted: \begin{isabelle} \isacommand{lemma}\ Suc_Suc_even_imp_even:\ "Suc\ (Suc\ n)\ \isasymin \ even\ \isasymLongrightarrow \ n\ \isasymin \ even"\isanewline -\isacommand{by}\ (drule\ even_imp_even_minus_2, \isacommand{apply}\ simp) +\isacommand{by}\ (drule\ even_imp_even_minus_2, simp) \end{isabelle} We have just proved the converse of the introduction rule \isa{even.step}.