public sumExpressionNode(termNode term)
 {
     this.term = term;
 }
 public termNode(termNode term, MulOpNode MulOp, powExpressionNode powExpression)
 {
     this.term          = term;
     this.MulOp         = MulOp;
     this.powExpression = powExpression;
 }
 public sumExpressionNode(sumExpressionNode sumExpression, sumNode sum, termNode term)
 {
     this.sumExpression = sumExpression;
     this.sum           = sum;
     this.term          = term;
 }