private function rotateLeft()
    {
        $right = $this->right;

        if ($right->information & 2) {
            $this->right = $right->left;
            $right->left = $this;
        } else {
            $right->information |= 2;
            $this->information &= ~ 1;
        }

        $this->information -= 4;

        if ($right->information >= 4) {
            $this->information -= $right->information & ~3;
        }

        $right->information -= 4;

        if ($this->information < 0) {
            $right->information += $this->information & ~3;
        }

        return $right;
    }