More realistically, Stoll (1978) and Ho and Stoll (1981, 1983) assume that the dealer is a risk-averse liquidity provider who absorbs temporary imbalances in the order flow. The dealer therefore often holds an inventory of assets that deviates from the desired portfolio position. Since he bears the risk of price fluctuations, the dealer requires compensation in terms of a bid–ask spread. Stoll (1978), Amihud and Mendelson (1980) and Ho and Stoll (1980, 1981, 1983) are the first models that formalize this idea. Biais (1993) also introduces incomplete information about the other dealers’ inventory positions.

In the following section we introduce Stoll’s modelling approach to inventory costs, which considers a one-dealer market, and then extend the model both on the supply side (by introducing a number of competitive dealers) and on the demand side (by allowing for a rational customer who trades both for risk-sharing and to speculate on his private information). The model is then further extended by assuming that liquidity suppliers and liquidity demanders both behave non-competitively and hence take the price impact of their net demand into account.

Here, you will find a cornucopia of places where products in the category you are searching are being sold. The same stores that you have just visited will likely have links on the Internet. So, why bother to go out to the stores in the first place? Because you want to actually see the similar products that are on store shelves. And, you want to gather the information that you can get from the product labels. If you should find a product that is offered for the same purpose as your idea, you can inspect it closely to see if your idea is an improvement on that product. Also, retailers do not usually have every product that is in their stores on their websites, so it is important to make sure that you do not overlook something by failing to make that trip to the store.

Individuals often make and sell products on the Internet that are offered nowhere else. If you neglect to do a good Internet search, you will miss this prior art. What is prior art?

If an active patent covers a product, you cannot legally make and sell it.

If that patent has expired, that product is said to be in the public domain and is now available to anyone to make and sell.

A product that has never been patented but has been offered for sale to the public is also said to be in the public domain and can never be patented.

All of the above examples are prior art; products that have already been presented to the public and cannot now be patent protected. One of the first things the examiners at the patent office will do when they begin with your application is to initiate a thorough search for prior art. If you failed to find these products but they were found in subsequent searches related to your patenting efforts, your patent would be rejected and you would have spent your money and your time in vain. It pays to be meticulous in your Internet  searching.