Group is
      $/basis.cm
      $/regexp-lib.cm
      handin/adder.sml  (* the student submission *)
      support/adder.sig (* the ADDER signature *)
      support/timer.sml
      helper.sig (* the HELPER signature *)
      helper.sml (* the Helper module *)
      checks.sig (* the CHECKS signature *)
      checks.sml (* the ChecksHelper functor *)
      main.sml   (* the big cheese *)