Can a company handle 70% of all bitcoin trading? In this paper about Mt. Gox, it is said that:


  By 2013, it was handling 70% of all bitcoin trading.


Doesn't it contradict the 51% rule, saying that if a single agent controls 51% of the bitcoin market, it will collapse?
@MaxSan is correct. Mt. Gox was only an exchange where people would buy and sell bitcoin. The 51% rule applies to a single entity (miner/pool) have 51% of the hashing power of the entire bitcoin mining network.