Assigning subjects to days according to their difficulty level

[umid]

Does subject difficulty concept exist in this system? If it does how can one assign subjects by their difficulty to certain time slots (e.g. phycics and math are rated to be more difficult than foreign language and history: dif(physics)=dif(math)> dif(history)>dif(for.lang) and one would like to assign classes by these ratings)?

[Liviu Lalescu]

If I understand correctly, you could use preferred times constraints (if you want for instance more difficult activities earlier).