src/HOL/Tools/Sledgehammer/sledgehammer_isar.ML

 
 fun hammer_away override_params subcommand opt_i fact_override state =
   let
     val ctxt = Proof.context_of state
     val override_params = override_params |> map (normalize_raw_param ctxt)
+    val _ = Isabelle_System.mkdir (Path.explode (getenv "ISABELLE_TMP"))
   in
     if subcommand = runN then
       let val i = the_default 1 opt_i in
         run_sledgehammer (get_params Normal ctxt override_params) Normal i
                          fact_override (minimize_command override_params i)