input: Write a function to determine if two given strings are anagrams. If they are, return True; otherwise, return False. If either of the strings is empty, return False.
  assert is_anagram("abcd", "dcba")==True
  assert is_anagram("listen", "silent")==True
  assert is_anagram("hello", "world")==False
  assert is_anagram("", "nonempty")==False
  assert is_anagram("anagram", "")==False
output: def is_anagram(s1, s2):
      if s1 == "" or s2 == "":
          return False
      return sorted(s1) == sorted(s2)