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The Supreme Court decision Silicon Valley is reading

Clarence Thomas testifies to Congress
Supreme Court Justice Clarence Thomas. Photo: Alex Wong/Getty Images

The ripples of a Monday Supreme Court ruling in favor of American Express could be felt on the West Coast, with some arguing it would make it harder for antitrust enforcers to take on big online platforms like Google, Facebook and Amazon.

Why that matters: Many of tech’s most profitable firms have created two-sided markets: Google and Facebook serve consumers on one side and marketers on another. Uber links up riders and drivers. Amazon serves customers and also the merchants who use its platform. All these situations make defining a monopoly more difficult.