Libra, the cryptocurrency backed by Facebook (and the other members of the Libra association) was announced yesterday. The web site and the white paper refer to the new currency as a stable currency: "Libra is designed to be a currency where any user will know that the value of a Libra today will be close to its value tomorrow and in the future." The stability is guaranteed by the intrinsic value of the coin, a result of the assets that back the value of the currency. These assets are called the "Library Reserve". The white paper refers to the similarities of this mechanism and the currency board that some currencies with fixed exchange rates use: "...the mechanics of interfacing with our reserve make our approach very similar to the way in which currency boards (e.g., of Hong Kong) have operated. Whereas central banks can print money at their own discretion, currency boards typically only print local currency when there are sufficient foreign exchange asse...