code: @Override
      public String parameters() {
          StringBuilder result = new StringBuilder();
          Iterator<Pair> it = xy.iterator();
          while (it.hasNext()) {
              Pair pair = it.next();
              result.append(String.format("%s %s",
                      Op.str(pair.getX()), Op.str(pair.getY())));
              if (it.hasNext()) {
                  result.append(" ");
              }
          }
          if (!Op.isEq(height, 1.0)) {
              result.append(String.format(" %s", Op.str(height)));
          }
          return result.toString();
      }
docs: Returns the parameters of the term as `x1 y1 xn yn [height]`
  
  @return `x1 y1 xn yn [height]`