input: Write a function to determine if a given string is a palindrome. A palindrome is a string that reads the same forward and backward. The function should convert the input string to lowercase and compare characters from both ends moving towards the center. If all characters match, return True; otherwise, return False.
  
  def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True
  
  assert is_palindrome("racecar")==True
  assert is_palindrome("Able, was I ere I saw Elba")==True
  assert is_palindrome("hello")==False
  assert is_palindrome("")==True
output: def is_palindrome(s):
    s = s.lower()
    left = 0
    right = len(s) - 1
    
    while left < right:
      if s[left] != s[right]:
        return False
      left += 1
      right -= 1
    return True