public function clear($index)
 {
     return $index < $this->left->getSize() ? $this->left->clear($index) : $this->right->clear($index - $this->right->getSize());
 }
 public function clear($index, $source = null)
 {
     return $index < $this->left->getSize() ? $this->left->clear($index, $source) : $this->right->clear($index - $this->right->getSize(), $source);
 }