We're tracking supplies for the hotel like food and soap. We want to create stock alerts. In our system, we specify low and high inventory levels, and we will create an alert when a transaction: * Changes the inventory from above or equal to the low level to below the low level * Changes the inventory from below or equal to the high level to above the high level * Results in a negative inventory. This includes going from negative to negative A transaction can only generate one alert. See the last transaction in the example.