= b command
        .set destination to the previous line of "b" command line,
         then exexute "a" command.
         See "a" command for effect of n,b,s.

        .copy just before the line.

            c3     |A
            0000002|B
            0000003|C
            0000004|D
            0000005|E
            b      |F
            0000007|G
        ===>
            0001000|A
            0002000|B
            0003000|C
            0004000|D
            0005000|E
            0005100*A
            0005200*B
            0005300*C
            0006000|F
            0007000|G