Some exchanges face banking issues and so can't hold fiat moneys. Instead they turn to a centralized cryptocurrency called Tether which is pegged to the price of the dollar. There are claims that this currency is not backed by real USD and that it is being used to manipulate cryptocurrency markets.
One persistent online critic, going by the screen name Bitfinex’ed, has written several very detailed essays on Medium arguing that Bitfinex appears to be creating Tether coins out of thin air and then using them to buy Bitcoin and push the price up.
A bearer instrument is a document that entitles the holder of the document rights of ownership or title to the underlying property, such as shares or bonds. Bearer instruments differ from normal registered instruments, in that no record is kept of who owns the underlying property, or of the transactions involving transfer of ownership. Whoever physically holds the bearer document is assumed to be the owner of the property. This is useful for investors and corporate officers who wish to retain anonymity, but ownership (or legal entitlement) is extremely difficult to establish in event of loss or theft.
Stated simply, Alice and Bob are in Nash equilibrium if Alice is making the best decision she can, taking into account Bob's decision while Bob's decision remains unchanged, and Bob is making the best decision he can, taking into account Alice's decision while Alice's decision remains unchanged. Likewise, a group of players are in Nash equilibrium if each one is making the best decision possible, taking into account the decisions of the others in the game as long as the other parties' decisions remain unchanged.
the administration’s report has come under withering scrutiny from Dr. Theodore Postol, a professor emeritus of science, technology, and national-security policy at the Massachusetts Institute of Technology, who once served as a scientific adviser to the chief of naval operations at the Pentagon.
Ripple is actually a company, but they created a cryptocurrency called XRP. XRP is pre-mined meaning all coins were created at once and then distributed or sold to various parties. XRP solves the double-spend problem differently than bitcoin, there is no proof of work. Whereas Bitcoin's origins are philosophically opposed to existing financial infrastructure and bitcoinattempts to route around it, Ripple and XRP are aimed at improving existing financial infrastructure via cryptocurrency tech.