def _intersection(la: list, lb: list):
    """
    Calculates an intersection between two lists of relations.
    """
    tmp = lb[:]
    cnt_tp, cnt_fn = 0, 0
    for a in la:
        if a in tmp:
            cnt_tp += 1
            tmp.remove(a)
        else:
            cnt_fn += 1

    return cnt_tp, cnt_fn