//    PG (621)

//    For the previous example, consider the sequence f0, f1....f6

//    For lam = 3,

//        (f0,.....f6) = (1,-1,0,1,-1,0,1)

//    The corresponding sequence of signs is 

//        (+,-,+,+,-,+,+)

//    and s(3) = 2