clarified ML option vs. Scala option (see also caa182bdab7a);
(*** Isabelle/Pure bootstrap: initial setup ***)
ML_file "ML/ml_statistics.ML";
ML_file "General/exn.ML";
ML_file "General/output_primitives.ML";
ML_file "Concurrent/thread_attributes.ML";
ML_file "Concurrent/thread_data.ML";
ML_file "Concurrent/thread_position.ML";
ML_file "ML/ml_recursive.ML";