BRUSSELS: Slovenia converted to the euro Monday, officially becoming the 13th member of the euro zone — and the first among the newest EU members to qualify to use the currency. But at least half a dozen other European mini-states and territories are using the currency as legal tender — without approval from the European Central Bank. The euro was introduced five years ago to provide economic cohesion among EU countries. But euros also are in circulation in dozens of countries and overseas territories from the North Atlantic to the Pacific. In Europe, Montenegro, Vatican City, San Marino and the...