If I accidentally close the window for the Interactive Exercise Solver, the program remains open but there's nothing you can do. If you go to "File | Open..." nothing happens, presumably because the Interactive Exercise Solver is shut down. You have to quit the application and start over if that happens. There should be a way to get the Interactive Exercise Solver back once you've accidentally closed it. (If there is, I couldn't find it.)
If I accidentally close the window for the Interactive Exercise Solver, the program remains open but there's nothing you can do. If you go to "File | Open..." nothing happens, presumably because the Interactive Exercise Solver is shut down. You have to quit the application and start over if that happens. There should be a way to get the Interactive Exercise Solver back once you've accidentally closed it. (If there is, I couldn't find it.)