announced that they would expand their asset purchase program by $1.4 trillion in two years. The Bank of Japan hopes to bring Japan from deflation to inflation, aiming for 2% inflation. The number of purchases is so large that it is expected to double the money supply, but this move has sparked concerns that the authorities in Japan are deliberately devaluing the yen to boost exports. However, the commercial sector in Japan worried that the devaluation would trigger an increase in import prices, especially for energy and raw materials. Redenomination proposals Numerous proposals have been made since the 1990s to redenominate the yen by introducing a new unit or new yen, equal to 100 yen, and nearly worth one U.S. dollar. This has not happened to date, since the yen remains trusted globally despite its low unit value, and due to the huge costs of reissuing new currency and updating currency-reading hardware. The negative impact of postponing upgrades to various computer software until redenomination occurs, in particular, was also cited. Coins Coins were introduced in 1870, in silver 5, 10, 20 and 50 sen and 1 yen, and gold 2, 5, 10 and 20 yen. Gold 1 yen were introduced in 1871, followed by copper 1 rin, , 1 and 2 sen in 1873. Cupronickel 5 sen coins were introduced in 1889. In 1897, the silver 1 yen coin was demonetized and the sizes of the gold coins were reduced by 50%, with 5, 10 and 20 yen coins issued. After 1920, all previous series of silver coins were discontinued in favor of cupro-nickel 10 sen and reduced-size silver 50 sen coins. Production of silver 50 sen coins ceased in 1938, after which a variety of base metals were used to produce 1, 5 and 10 sen coins during the Second World War. Clay 5 and 10 sen coins were produced in 1945, but not issued for circulation. After the war, brass 50 sen, 1 and 5 yen were introduced between 1946 and 1948. The current-type holed brass 5 yen was introduced in 1949, the bronze 10 yen in 1951, and the aluminum 1 yen in 1955. Coins in denominations of less than 1 yen became invalid on December 31, 1953, following enforcement of the . In 1955 the first unholed, nickel 50 yen was introduced. In 1957, silver 100 yen pieces were introduced, followed by the holed 50 yen