In this era of recession - I wrote that nine months ago, and it is still true! - it is important that we all be good consumers and keep the economy moving. The macro-economic knowledge base of Supplement 2 showed what happens when we fail. So, bearing this in mind, the buildings all concern buying and selling, as you may have guessed from their names.
There are three kinds of building: wholesalers, retailers, and fuel-stations. Each retailer sells one (and one only) of five types of good to the public: coal, diamonds, glasses (tableware, not eyewear), peaches, and televisions. The retailers buy their stocks from traders, who in turn buy from wholesalers. By buying cheap at a wholesaler and selling dear to a retailer, a smart trader can make a hefty profit. Wholesalers, retailers, and fuel-stations are described by the facts below:
sells(B,Good,Price): B names a wholesaler, and will be one of the names given as the first argument of
building. Good is the type of product sold. Like retailers, each wholesaler deals in only one kind of product. Price is the price at which the wholesaler sells one unit of the product to a trader (i.e. the price at which the trader buys it).
buys(B,Good,Price): B names a retailer. As before, Good is the product type. This time, Price is the price at which the retailer buys from the trader, i.e. the price at which the trader sells it.
sells_fuel(B,Price): This tells you which buildings are fuel stations. Price is the price per unit of fuel, and B is the name of the building.