src/HOL/Tools/ATP/atp_systems.ML

       (fn systems => (if null systems then get_systems () else systems)
                      |> `(find_system name versions))
 
 fun the_system name versions =
   case get_system name versions of
-    NONE => error ("System " ^ quote name ^ " not available at SystemOnTPTP.")
-  | SOME sys => sys
+    SOME sys => sys
+  | NONE => error ("System " ^ quote name ^ " not available at SystemOnTPTP.")
 
 fun remote_config system_name system_versions proof_delims known_failures
                   default_max_relevant use_conjecture_for_hypotheses
                   : prover_config =
   {exec = ("ISABELLE_ATP", "scripts/remote_atp"),