def check_unbinding(graph):
    """
    check rule unbinding

    :param graph: a StrandGraph object
    :return: edges to be deleted
    """
    changeedge = []
    for i in graph.E:
        if graph.check_toehold(i):
            if not graph.anchored(i):
                print("RU: " + str(i.copy()))
                changeedge.append(i)
    return changeedge