def _trapz_simps_overlap2(dy, dx):
    """Correction term in the squared error when combining trapezoidal and Simpson's rule.

    Only exact for equal spacing *dx* left and right of *dy*.

    err^2 = (h/6)^2 ((3 Df0)^2 + ((3+2)Df1)^2 + (8Df2)^2 + (4Df3)^2 + ...)
                      |-- trapz ---| |--------- Simpson ---------------

    (3+2)^2 = 3^2 + 2^2 + 12    <--- 12 is the "overlap" correction
    """
    return (dx/6)**2 * 12 * dy**2