def show_twolightcones(eca, cell1, cell2, color1=None, color2=None, color3=None
    ):
    """Shows two light cones.

    The intent is to highlight the intersection of two light cones.

    Parameters
    ----------
    cell1, cell2 : 2-tuple
        A 2-tuple (t, s) where t is the row index and s is the column
        index of the cell.

    color1 : Matplotlib color
        The color to use for cell1's light cone.
    color2 : Matplotlib color
        The color to use for cell2's light cone.
    color3 : Matplotlib color
        The color to use for the intersection of the light cones of
        cell1 and cell2.

    """
    pass
