src/Sequents/prover.ML

      [Pretty.big_list "safe rules:" (map (Display.pretty_thm ctxt) safes),
       Pretty.big_list "unsafe rules:" (map (Display.pretty_thm ctxt) unsafes)]
   end;
 
 val _ =
-  Outer_Syntax.command @{command_spec "print_pack"} "print pack of classical rules"
+  Outer_Syntax.command @{command_keyword print_pack} "print pack of classical rules"
     (Scan.succeed (Toplevel.keep (Pretty.writeln o pretty_pack o Toplevel.context_of)));
 
 
 (* declare rules *)