Write a function that checks if a given word stored in a doubly linked list is a palindrome.

<?php

class Node {

        public $value;

        public $next = null; // next node

        public $prev = null; // previous node

        public function __construct($value) {
                $this->value = $value;
        }
}

class Palindrome {

/**
•@param string $word
•@return bool */

        public static function isPalindrome($head, $tail){
                
                if ($head == null)  
                        return true; 
                  
                while ($head != $tail){
                        if ($head->value != $tail->value)  
                                return false; 
          
                        $head = $head->next; 
                        $tail = $tail->prev;  
                }   
                return true;
        }
}

$head = new Node(1);

$firstNode = new Node(2);

$secondNode = new Node(3);
$tail = new Node(4);

$head->next = $firstNode;
$firstNode->prev = $head;

$firstNode->next = $secondNode;

$secondNode->prev = $firstNode;
$secondNode->next = $tail;

echo Palindrome::isPalindrome($head, $tail);