input: Write a python function to check if a word is a palindrome.
  assert is_palindrome('madam') == True
  assert is_palindrome('racecar') == True
  assert is_palindrome('hello') == False
  assert is_palindrome('level') == True
  assert is_palindrome('world') == False
output: def is_palindrome(word):
      return word == word[::-1]