According to a May 15 federal court filing in Washington state, Amazon alleges that Discovery's online retail store violates four patents Amazon holds on search refinements, specifically, how users can get recommendations or search for products based on what they previously bought on the site.

If "Amazon Vs. Discovery" in a patent infringement lawsuit sounds familiar, that's because it is: back in March, Discovery filed suit against Amazon alleging that Amazon's Kindle violates electronic book patents its held since November 2007.

"The Kindle and Kindle 2 are important and popular content-delivery systems," said Joseph A. LaSala Jr., Discovery Communications' general counsel, in a statement at the time. "We believe they infringe on intellectual property rights, and that we are entitled to fair compensation. Legal action is not something Discovery takes lightly."

In a separate May 15 filing, however, in U.S. District Court in Delaware, Amazon refutes Discovery's e-book patent allegation, indicating the Discovery patent in question was not only not infringed, but also invalid. Amazon appears to accuse Discovery of withholding information that mislead the U.S. Patent and Trademark Office.

A statement sent to Seattle-based tech blog TechFlash and other outlets by Discovery reads: "Discovery remains committed to protecting its intellectual property assets and we have continued confidence in the merits of our case. We look forward to vindicating our position in court."

In a separate statement, an Amazon spokesman, Craig Berman, said, "Amazon.com continues to deny Discovery's allegations of wrongdoing and we will vigorously defend ourselves."

En garde!