It's a deja vu, I remembered I read it in somewhere,
it turned out ZeroHedge report that 3 months ago.
The story is excerpted from a book called "Dark Pools: High-Speed Traders, A
.I. Bandits, and the Threat to the Global Financial System" http://www.zerohedge.com/news/dark-pool-truth-about-what-really
that should thank to the stupid SEC rule.
it abandons "locked market", but allows a order type that makes "dark"
locked market. there is nothing wrong with high fequency trading firms.