[gus_massa]

Near the bottom of the article:

> One clue might lie in Anne's decoding machine. Figuring out which other bit of information A is entangled with is an extraordinarily complicated problem. [...] In 2013 they calculated that, even given the fastest computer that the laws of physics would allow, it would take Anne an extraordinarily long time to decode the entanglement. By the time she had an answer, the black hole would have long evaporated, disappearing from the universe and taking with it the threat of a deadly firewall.

The "machine" is an oversimplification, but I don't understand the equivalent experiment that can distinguish between B and C.

Also, there are more complicated situations. You can entangle 3, 4, ... or more particles http://en.wikipedia.org/wiki/Multipartite_entanglement

Usually the discussions are only about entanglement of 2particles, because that is weird enough, but the math for more particles is just a little more complicated.