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public SubListInterface listOfOperators()  {    SubListInterface sl = DataFactory.makeSubList();    if(!this.isTerm())    {      this.leftT.listOfOperators();      sl = this.listOfOperators(sl);      this.rightT.listOfOperators();    }    return sl;  }    private SubListInterface listOfOperators(SubListInterface sl)  {    SubListInterface sl2 = sl;    while(!sl2.isEmpty())    {      sl2 = sl2.getRemainder();    }    sl2.setRootItem(this.operator);    sl2.attachRemainder(DataFactory.makeSubList());    return sl;  }