anchor.diff:  
     E removeAt(int index) {
       E result = this[index];
  -    _closeGap(index, index + 1);
  +    setRange(index, this.length - 1, this, index + 1);
  +    length--;
       return result;
     }
   
  
positive.code: 
    void removeRange(int start, int end) {
      RangeError.checkValidRange(start, end, this.length);
      if (end > start) {
        _closeGap(start, end);
      }
    }
  
    void fillRange(int start, int end, [E fill]) {
  
negative.code:   bool remove(Object element) {
      for (int i = 0; i < this.length; i++) {
        if (this[i] == element) {
          this.setRange(i, this.length - 1, this, i + 1);
          this.length -= 1;
          return true;
        }
      }
      return false;
    }
  
    void removeWhere(bool test(E element)) {
  