src/HOL/Isar_examples/ExprCompiler.thy

   fix x xs;
   assume "??P xs";
   show "??P (x # xs)" (is "??Q x");
   proof (induct ??Q x type: instr);
     fix val; show "??Q (Const val)"; by brute_force;
-    next;
+  next;
     fix adr; show "??Q (Load adr)"; by brute_force;
-    next;
+  next;
     fix fun; show "??Q (Apply fun)"; by brute_force;
   qed;
 qed;
 
 lemma exec_comp:
   "ALL stack. exec (comp e) stack env = eval e env # stack" (is "??P e");
 proof (induct ??P e type: expr);
-
   fix adr; show "??P (Variable adr)"; by brute_force;
-  next;
+next;
   fix val; show "??P (Constant val)"; by brute_force;
-  next;
+next;
   fix fun e1 e2; assume "??P e1" "??P e2"; show "??P (Binop fun e1 e2)";
     by (brute_force simp add: exec_append);
 qed;