src/Pure/ML/ml_console.scala

 
   def main(args: Array[String]): Unit = {
     Command_Line.tool {
       var dirs: List[Path] = Nil
       var include_sessions: List[String] = Nil
-      var logic = Isabelle_System.getenv("ISABELLE_LOGIC")
+      var logic = Isabelle_System.default_logic()
       var modes: List[String] = Nil
       var no_build = false
       var options = Options.init()
       var raw_ml_system = false