Jane Street had gone from a few traders with a few million dollars, in 1999, to roughly two hundred traders working with several billion dollars, in 2014. One big reason was ETFs, whose global value had grown from less than $100 billion to $2.2 trillion (on its way to more than $10 trillion in 2022). When ETFs changed hands, Jane Street was often present to take an ant-bite-sized piece of the transaction. The role of the Jane Street trader—one of the biggest sources of profits—was to keep the prices of all of these ETFs in line with the assets inside of them. The price of any pool of assets
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