==== 2024-09-07 ====
Notes from \\
https://www.wsj.com/articles/high-frequency-trader-hudson-river-to-execute-retail-stock-trades-11625047200?mod=itp_wsj&ru=yahoo \\
High-Frequency Trader Hudson River to Execute Retail Stock Trades \\
2021-06-30
  * Hudson River Trading LLC
    * one of the biggest high-frequency trading firms
    * handles around 8% of daily U.S. stock-trading volume
    * based in New York
    * founded in 2002
    * 500 employees around the world
    * maintains a low profile
    * a proprietary trading firm that manages its own money and doesn’t take outside capital
    * active in stocks, options, futures, currencies, bonds and cryptocurrencies
    * rivals: Citadel Securities, Virtu Financial Inc

  * Hudson River Trading LLC is building a retail wholesaler business
  * Citadel and Virtu handle more than 70% of individual investors’ stock orders

  * major retail wholesalers: Citadel Securities, Virtu, Susquehanna, Two sigma, UBS, Jane Street

  * Wolverine Holdings LP
  * wholesaler business requires trading firms to set up sales relationships with brokerages and transact in a broad array of stocks and etfs favored by small investors

Notes from https://www.sikorskaya.net/files/Bryzgalova_Pavlova_Sikorskaya_2023.pdf

pg-3 (of pdf)
  * although only a fraction of investors trade options, most of the PFOF received by retail brokerages comes from options, not equities
  * For example, in 2021, U.S. brokerages received \$2.4 billion in PFOF for options and only \$1.3 billion for equities.
  * The lion’s share of PFOF for options came from only three wholesalers: Citadel, Susquehanna, and Wolverine.

pg-11 (of pdf)
  * Figure 1 plots aggregate monthly payments for order flow received by U.S. retail brokerages.
    * shows that the brokerages consistently received more PFOF from options than stocks
  * Figure 2 shows the market concentration in PFOF for options as well as stocks. The top 5 have O(90%) share.

pg-54 (of pdf)
  * reports the total PFOF in stocks and options for each broker-firm pair in Q1/2020 - Q4/2021