def find_bidirectional_reactions(va, tolerance=1e-08):
    """
    Returns the ids of reactions that can both carry net flux in the forward or
    backward direction.

    :param va: A variability analysis, pandas Dataframe like so:
                                          maximum       minimum
                6PGLter             -8.330667e-04 -8.330667e-04
                ABUTt2r              0.000000e+00  0.000000e+00
                ACALDt               0.000000e+00  0.000000e+00

    :return:
    """
    return va[va['minimum'] * va['maximum'] < -tolerance]
