Is any proof out there that exchanges have actually provided real usd to exchange for the usdt tokens? and where does this usd come from - exchanges offering usdt do not offer usd trading nor .deal directly with usd fiat from customers in any way. If the exchanges are selling crypto for usd some place outside of their own exchange then using that usd to attain usdt is there any proof of this? because if all we have is the theory that this is how it's supposed to work, that doesn't cut it.