The problem with this however was that the dominant firms would face higher costs than competitors.

A dominant firm cannot sign contracts with its distributors that require them to buy one product as a condition of getting another product.

Taking down Microsoft may simply mean exchanging one dominant firm with another.

Markets driven by technical standards or by "network effects" can give the dominant firm a near-monopoly.

"Courts these days are taking a microscopic view of the conduct of dominant firms," he said.

It is difficult to prove at what point a dominant firm's prices become "exploitative" and this category of abuse is rarely found.

In the medium to long term, price wars can be good for the dominant firms in the industry.

The dominant firm sets prices which are simply taken by the smaller firms in determining their profit maximizing levels of production.

Even a dominant firm will face rivals seeking to find a window of opportunity to chip away at the dominant position.

Microsoft disputes the monopolist label, but argues that the rules for dominant firms are not much different.