def get_bmap(net, m, bmap):
    """
    Updates the B-map with the invisibles enabling marking m

    Parameters
    --------------
    net
        Petri net
    m
        Marking
    bmap
        B-map

    Returns
    --------------
    trans_list
        List of invisibles that enable m
    """
    if m not in bmap:
        bmap[m] = []
        for t in net.transitions:
            if t.label is None:
                if m <= t.out_marking:
                    bmap[m].append(t)
    return bmap[m]