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Some crypt exchanges sell “long” bitcoin derivatives contracts, with which traders bet that prices will rise without buying any coin.

Hong Kong bars retail investors from accessing crypto funds; Europe has had stiff restrictions since last year.

Two other features can make losses catastrophic: leverage (platforms typically allow derivative traders to borrow between two and 100 times what they put in) and high trading costs.

In any case, says Danny Masters of CoinShares, which sells crypto vehicles, the regulator should not be choosing which technology thrives or fails.