So long as the landlord does not contract with them and does not demand or accept rent from them, the landlord need not let subtenants cure the tenant’s rent default.  Accordingly, the landlord’s 3-day notice to quit served on the subtenants was proper though it did not offer them the alternative of curing the tenant’s rent default.  Also, under San Francisco’s Rent Stabilization Ordinance, once the tenant defaulted and his lease was terminated, the landlord could demand full market rent from the subtenants if the chose to remain in the apartment.