Market share - monopoly - two key players simple explanatory

Excel spreadsheet. A simple explanatory example of a market in which there are only two main players, Us and Them, where Us have come on to the market and in a decade have taken over the market from Them. There is also a couple of minor players Other and New. Includes simple numbers, but realistic, when one company tends to dominate the market you could see an example just like this, and they are becoming more and more likely, a couple of examples of useful Chart representation of market share and a couple of possible problems and how to overcome them.