old_contents: VAR_LABELS = {'Y': 'GDP ($Y_t$)', 'C': 'Consumption ($C_t$)',
                'K': 'Capital Stock ($K_t$)', 'L': 'Labor ($L_t$)'}
  
  ToGDP_LABELS = {'D': 'Debt-to-GDP ($D_{t}/Y_t$)'}
  
new_contents: VAR_LABELS = {'Y': 'GDP ($Y_t$)', 'C': 'Consumption ($C_t$)',
                'K': 'Capital Stock ($K_t$)', 'L': 'Labor ($L_t$)',
                'nssmat': 'Labor Supply', 'n_mat': 'Labor Supply'}
  
  ToGDP_LABELS = {'D': 'Debt-to-GDP ($D_{t}/Y_t$)'}
  
subject: add more labels