def Iaxn(mt, x, n, *args):
    """ during a term certain, IAn """
    return (Sx(mt, x + 1) - Sx(mt, x + n + 1) - n * Nx(mt, x + n + 1)) / Dx(mt, x)
def Iaxn ( mt , x , n , * args ) : return ( Sx ( mt , x + 1 ) - Sx ( mt , x + n + 1 ) - n * Nx ( mt , x + n + 1 ) ) / Dx ( mt , x )
during a term certain, IAn