print_result([H|Trace], Prev, Time) ->
  print_swap(Swap, H),
  Interval = Time + crossing_time(Swap),
  print_result(Trace, H, Interval).

print_swap(Swap, To) ->
  case To band 1 of
    0 ->
      io:format(  "    ~s -->~n", [display(Swap)]);
    1 ->
      io:format(  "<-- ~s~n", [display(Swap)])
  end.