input: Write a python function to check if a sentence is a palindrome.
  assert is_palindrome("Anna went to vote in the election.") == False
  assert is_palindrome("A man a plan a canal Panama") == True
  assert is_palindrome("No lemon no melon") == True
output: def is_palindrome(sentence):
      cleaned_sentence = ''.join(char.lower() for char in sentence if char.isalnum())
      return cleaned_sentence == cleaned_sentence[::-1]