sigmoid: sigmoid-in-range

    description:
        sigmoid-in-range[a,b] ket
        the in-range sigmoid
        if a <= x <= b, return x
        else return 0

    examples:
        sigmoid-in-range[2,4] (|a> + 2|b> + 3|c> + 4|d> + 5|e>)
            0|a> + 2|b> + 3|c> + 4|d> + 0|e>

    see also: