有4个字母：U、C、D、V，它们可以相加，也能产生进位，如图3-7所示：V+V=V，U+D=V，但他要进U位现有2个由上述字母构成的“数”（五位），只对第2个数进行操作，有3种操作。-Has four letters: U, C, D, V, they can add up, but also can produce binary, 3-7 shown in Figure: V+ V = V, U+ D = V, but he want into the U-bit is have two letters from the above constitute a " few"　(five), only the number 2 on the first operation, there is three kinds of operations.