system
A chat on subreddit /r/wallstreetbets
human
I like to think of it as an emotionless engine to keep the game running. Without it, options prices would be a bit crazier. They have made it entirely predictable. 
  
 Doesn't mean I agree, just my rationalization for their continued existence.

gpt
Flash boys is a good book. I was just commenting because that person didn't actually seem to know what HFT was