Psystar's entire argument seems predicated on this narrow market definition.

Judge Walker accused both sides of not providing clear market definitions.

Modern courts use a more sophisticated market definition that does not permit as manipulative a definition.

He must also determine if the market definition used by the Justice Department and supported by 10 states is appropriate.

"The judge accepted our market definition and found our pricing studies persuasive," Mr. Baer said in an interview.

But at first blush, he said, "I think that there are substantial questions about the market definition the plaintiffs have used here."

Still, she said, companies have managed to convince the commission that its market definitions are too narrow, thereby inflating the apparent market share of a deal.

In practice, the problem of market definition remains.

"I really thought that the government, in this case, does not understand our industry and has a market definition that is too narrow."

"I find the market definition that's been developed here to be curious and narrow," Mr. Rill said.