Why don't you read through the paper?

Here is the short answer:

> We adopt the definition of regulated exchanges from the state of New York, which has one of the earliest regulatory frameworks in the world. [6]

> 6 Regulated exchanges are issued BitLicenses and are regulated by the New York State Department of Financial Services. Bitlicence carries some of the most stringent requirements. Our main results are robust to alternative classifications of regulated exchanges. As of June 2020, NYDFS has issued licenses to 25 regulated entities, six of which provide crypto exchange service. They are Itbit, Coinbase, Bitstamp, Bitflyer, Gemini, and Bakkt (futures and options only). Further information can be found at: https://www.dfs.ny.gov/apps_and_licensing/virtual_currency_b.... (Last accessed: July 3, 2020)