Relationships between products are fuzzier with software than with physical goods and services. One of the cases Lessig referred to several times was a well-known 1992 U.S. Supreme Court decision ruling which found that Kodak was guilty of tying.

Because Kodak manufactured certain machines but refused to provide necessary parts to other firms that wanted to service the machines, the court ruled Kodak had tied service on the machines to the equipment itself.

Jackson, who has been involved with the Microsoft litigation for more than three years, earned a reputation for looking into technical questions himself, rather than relying only on the parties involved.

In his brief, Lessig supported that philosophy: "I am not a skeptic of courts' ability to understand how software functions," he wrote.

Three weeks from now, the two sides will begin closing arguments, after which Jackson will rule on the legal questions of the case.

On Nov. 5, Jackson issued "findings of fact," which both sides agreed were unfavorable to Microsoft. In the findings, Jackson determined that Microsoft has "monopoly power" in the market for PC operating systems.

For now, the two sides are continuing negotiations under a mediator's watch. Lessig, who is on leave from HLS this year, is in Berlin and could not be reached yesterday.