def _line_exists(wavelengths, y, z, x0, xRes, fluxMin):
    """For a group of lines finds if the there is some change in flux greater
    than some minimum at the same redshift with different initial wavelengths

    Parameters
    ----------
    wavelengths : (N) ndarray
        array of initial wavelengths to check
    y : (N) ndarray
        flux array to check
    x0 : float
        wavelength of the first value in y
    xRes : float
        difference in wavelength between consecutive cells in flux array
    fluxMin : float
        maximum flux to count as a line existing.

    Returns
    -------

    flag : boolean
        value indicating whether all lines exist. True if all lines exist
    """
    for wl in wavelengths:
        redWl = (z + 1) * wl
        indexRedWl = (redWl - x0) / xRes
        if indexRedWl > len(y):
            return False
        if y[int(indexRedWl)] > fluxMin:
            return False
    return True
